Fix double free in XSPICE CALLBACK functions as desribed here:

https://sourceforge.net/p/ngspice/mailman/message/37677362/
and add missing CALLBACKs in models that use STATIC_VARs with
pointer values.

src/xspice/icm/analog/oneshot/cfunc.mod

@@ -51,6 +51,7 @@ NON-STANDARD FEATURES
 /*=== INCLUDE FILES ====================*/
 
 #include "oneshot.h"
+#include <stdlib.h>
 
 
 
@@ -85,6 +86,20 @@ typedef struct {
 
 
 
+static void
+oneshot_callback(ARGS, Mif_Callback_Reason_t reason)
+{
+    switch (reason) {
+        case MIF_CB_DESTROY: {
+            Local_Data_t *loc = STATIC_VAR (locdata);
+	    if (loc) {
+                free(loc);
+		STATIC_VAR (locdata) = NULL;
+	    }
+            break;
+        }
+    }
+}
 
 
 /*==============================================================================
@@ -253,6 +268,7 @@ void cm_oneshot(ARGS)  /* structure holding parms,
         /*** allocate static storage for *loc ***/
         STATIC_VAR (locdata) = calloc (1 , sizeof ( Local_Data_t ));
         loc = STATIC_VAR (locdata);
+	CALLBACK = oneshot_callback;
 
         /* Allocate storage for breakpoint domain & pulse width values */
         x = loc->control = (double *) calloc((size_t) cntl_size, sizeof(double));

src/xspice/icm/analog/pwl/cfunc.mod

@@ -232,9 +232,12 @@ cm_pwl_callback(ARGS, Mif_Callback_Reason_t reason)
             double *last_x_value = STATIC_VAR (last_x_value);
             double *x = STATIC_VAR (x);
             double *y = STATIC_VAR (y);
-            free(last_x_value);
+            if (last_x_value)
-            free(x);
+                free(last_x_value);
-            free(y);
+            if (x)
+                free(x);
+            if (y)
+                free(y);
             STATIC_VAR (last_x_value) = NULL;
             STATIC_VAR (x) = NULL;
             STATIC_VAR (y) = NULL;

src/xspice/icm/digital/d_genlut/cfunc.mod

@@ -65,6 +65,20 @@ NON-STANDARD FEATURES
 
 
 
+static void
+genlut_callback(ARGS, Mif_Callback_Reason_t reason)
+{
+    switch (reason) {
+        case MIF_CB_DESTROY: {
+            Digital_t *loc = STATIC_VAR (locdata);
+	    if (loc) {
+                free(loc);
+                STATIC_VAR (locdata) = NULL;
+            }
+            break;
+        }
+    }
+}
 
 
 /*==============================================================================
@@ -170,6 +184,7 @@ void cm_d_genlut(ARGS)
         /* allocate storage for the lookup table */
         STATIC_VAR (locdata) = calloc((size_t) tablelen, sizeof(Digital_t));
         lookup_table = STATIC_VAR (locdata);
+	CALLBACK = genlut_callback;
 
         /* allocate storage for the outputs */
         cm_event_alloc(0, osize * (int) sizeof(Digital_t));

src/xspice/icm/digital/d_lut/cfunc.mod

@@ -65,6 +65,20 @@ NON-STANDARD FEATURES
 
 
 
+static void
+lut_callback(ARGS, Mif_Callback_Reason_t reason)
+{
+    switch (reason) {
+        case MIF_CB_DESTROY: {
+            Digital_State_t *loc = STATIC_VAR (locdata);
+	    if (loc) {
+                free(loc);
+                STATIC_VAR (locdata) = NULL;
+            }
+            break;
+        }
+    }
+}
 
 
 /*==============================================================================
@@ -136,6 +150,7 @@ void cm_d_lut(ARGS)
         /* allocate storage for the lookup table */
         STATIC_VAR (locdata) = calloc((size_t) tablelen, sizeof(Digital_State_t));
         lookup_table = STATIC_VAR (locdata);
+	CALLBACK = lut_callback;
 
         /* allocate storage for the outputs */
         cm_event_alloc(0, sizeof(Digital_State_t));

src/xspice/icm/digital/d_state/cfunc.mod

@@ -1592,6 +1592,7 @@ static void callback(ARGS, Mif_Callback_Reason_t reason)
         if (table->next_state)
             free(table->next_state);
         free(table);
+	STATIC_VAR(table) = NULL;
     }
 }
                                         

src/xspice/icm/xtradev/pswitch/cfunc.mod

@@ -85,7 +85,10 @@ cm_pswitch_callback(ARGS, Mif_Callback_Reason_t reason)
     switch (reason) {
         case MIF_CB_DESTROY: {
             Local_Data_t *loc = STATIC_VAR (locdata);
-            free(loc);
+	    if (loc) {
+                free(loc);
+                STATIC_VAR (locdata) = NULL;
+            }
             break;
         }
     }

src/xspice/icm/xtradev/sidiode/cfunc.mod

@@ -96,7 +96,10 @@ cm_sidiode_callback(ARGS, Mif_Callback_Reason_t reason)
     switch (reason) {
         case MIF_CB_DESTROY: {
             Local_Data_t *loc = STATIC_VAR (locdata);
-            free(loc);
+	    if (loc) {
+                free(loc);
+                STATIC_VAR (locdata) = NULL;
+            }
             break;
         }
     }

src/xspice/icm/xtradev/zener/cfunc.mod

@@ -48,6 +48,7 @@ NON-STANDARD FEATURES
 /*=== INCLUDE FILES ====================*/
 
 #include <math.h>
+#include <stdlib.h>
 
                                       
 
@@ -70,6 +71,20 @@ NON-STANDARD FEATURES
 
 
 
+static void
+cm_zener_callback(ARGS, Mif_Callback_Reason_t reason)
+{
+    switch (reason) {
+        case MIF_CB_DESTROY: {
+            double *loc = STATIC_VAR(previous_voltage);
+	    if (loc) {
+                free(loc);
+                STATIC_VAR(previous_voltage) = NULL;
+            }
+            break;
+        }
+    }
+}
 
                    
 /*==============================================================================
@@ -180,6 +195,7 @@ void cm_zener(ARGS)  /* structure holding parms,
         /* Set previous_voltage value to zero... */
         *previous_voltage = 0.0;
 
+        CALLBACK = cm_zener_callback;
     }  
     else {