Corrected two "extresist" issues: (1) Prevent a segfault when

reading a resistor device which uses the syntax where the resistor
is given a value directly and not as a parameter;  (2) allow the
use of "extresist minres 0" (allow resistors in the output no
matter how small).  Thanks to Torleif Skaar for finding the issue
with the resistor syntax.

resis/ResReadExt.c

@@ -800,9 +800,11 @@ ResReadDevice(int argc,
      * be simpler if all devices just put "None" in this position.
      */
     n = argc - i;
-    if ((n % 3) == 1)	/* Device has a substrate argument */
+    if ((n % 3) == 1)
     {
-	if (strcmp(argv[i], "None"))
+	/* Device has a substrate argument or a numerical value */
+
+	if (strcmp(argv[i], "None") && (!StrIsNumeric(argv[i])))
 	{
 	    entry = HashFind(&ResNodeTable, argv[i]);
 	    device->subs = (ResExtNode *)HashGetValue(entry);

resis/ResRex.c

@@ -350,7 +350,7 @@ typedef enum {
 	    if (cmd->tx_argc > 2)
 	    {
 		resisdata->minres = MagAtof(cmd->tx_argv[2]);
-		if (resisdata->minres <= 0)
+		if (resisdata->minres < 0)
 		{
 		    TxError("Usage:  %s minres [value]\n", cmd->tx_argv[0]);
 			return;