verify pointer before utilization

src/frontend/inp.c

@@ -815,8 +815,10 @@ inp_spsource(FILE *fp, bool comfile, char *filename, bool intfile)
             /* now load deck into ft_curckt -- the current circuit. */
             inp_dodeck(deck, tt, wl_first, FALSE, options, filename);
 
-            ft_curckt->devtlist = devtlist;
-            ft_curckt->modtlist = modtlist;
+            if (ft_curckt) {
+                ft_curckt->devtlist = devtlist;
+                ft_curckt->modtlist = modtlist;
+            }
 
             /* inp_dodeck did take ownership */
             tt = NULL;

src/frontend/plotting/x11.c

@@ -1058,7 +1058,8 @@ X11_Input(REQUEST *request, RESPONSE *response)
 
     default:
         internalerror("unrecognized input type");
-        response->option = error_option;
+        if (response)
+            response->option = error_option;
         return 1;
         break;
     }

src/frontend/runcoms.c

@@ -342,7 +342,8 @@ dosim(
     if (rawfileFp) {
         if (ftell(rawfileFp) == 0) {
             (void) fclose(rawfileFp);
-            (void) unlink(wl->wl_word);
+            if (wl)
+                (void) unlink(wl->wl_word);
         } else {
             (void) fclose(rawfileFp);
         }