Save and restore GrDisplayStatus across long operations

CIFGenSubcells() and extSubtree() set GrDisplayStatus =
DISPLAY_IN_PROGRESS while they run a 5-second progress timer, then
unconditionally restore DISPLAY_IDLE on exit. In native builds the
initial state is always IDLE, so this is harmless. In WASM/headless
builds the null display driver sets DISPLAY_SUSPEND at startup, and
forcing IDLE at the end of these long operations destroys the
SUSPEND guard that protects WindUpdate() from running display
callbacks against a non-existent screen.

Save the previous status before overwriting and restore it on exit.
This is also reentrant-safe: nested DISPLAY_IN_PROGRESS scopes (e.g.
extract followed by gds write) now keep the outer state intact.

* cif/CIFhier.c — CIFGenSubcells
* extract/ExtSubtree.c — extSubtree

extract/ExtSubtree.c

@@ -174,8 +174,10 @@ extSubtree(parentUse, reg, f)
     int cuts, totcuts;
     float pdone, plast;
     SearchContext scx;
+    int savedDisplayStatus;
 
     /* Use the display timer to force a 5-second progress check */
+    savedDisplayStatus = GrDisplayStatus;
     GrDisplayStatus = DISPLAY_IN_PROGRESS;
     SigSetTimer(5);		    /* Print at 5-second intervals */
 
@@ -348,7 +350,7 @@ done:
     /* Output connections and node adjustments */
     extOutputConns(&ha.ha_connHash, f);
     HashKill(&ha.ha_connHash);
-    GrDisplayStatus = DISPLAY_IDLE;
+    GrDisplayStatus = savedDisplayStatus;
     SigRemoveTimer();
 
     /* Clear the CU_SUB_EXTRACTED flag from all children instances */