Added code to avoid a segfault if a resistor or capacitor is

specified without a list of substrate connection types, but
the "s=" parameter is used, resulting in an attempt to access a
substrate node that does not exist.

ext2spice/ext2hier.c

@@ -343,7 +343,11 @@ spcHierWriteParams(
 		break;
 	    case 's':
 		fprintf(esSpiceF, " %s=", plist->parm_name);
-		/*EFNode *subnodeFlat =*/ spcdevSubstrate(hc->hc_hierName,
+		if (dev->dev_subsnode == NULL)
+		    TxError("Error:  Device %s missing substrate node!\n",
+				EFDevTypes[dev->dev_type]);
+		else
+		    spcdevSubstrate(hc->hc_hierName,
 				dev->dev_subsnode->efnode_name->efnn_hier,
 				dev->dev_type, esSpiceF);
 		break;