Don't call DestroyGraph if graf id is 0

src/frontend/postsc.c

@@ -141,7 +141,7 @@ int PS_Init(void)
 
     if (settxcolor > maxcolor || settxcolor < 0) {
         fprintf(stderr, "Bad PS text color selection %d\n", settxcolor);
-        fprintf(stderr, "    Maximum for hcopypstxcolor is %d\n", maxcolor - 1);
+        fprintf(stderr, "    Maximum for hcopypstxcolor is %d\n\n", maxcolor - 1);
         colorflag = 0;
         dispdev->numcolors = 2;
     }
@@ -149,7 +149,7 @@ int PS_Init(void)
     if (setbgcolor > maxcolor || setbgcolor < 0) {
         fprintf(stderr, "Bad PS background color selection %d\n", setbgcolor);
         fprintf(stderr, "    Maximum for hcopypscolor is %d\n", maxcolor - 1);
-        fprintf(stderr, "    Set to 1 (white)\n");
+        fprintf(stderr, "    Set to 1 (white)\n\n");
         setbgcolor = 1;
     }
 
@@ -327,7 +327,8 @@ int PS_Close(void)
      * and reset currentgraph to graphid 1, if possible
      */
     if (!screenflag) {
-        DestroyGraph(hcopygraphid);
+        if (hcopygraphid > 0)
+            DestroyGraph(hcopygraphid);
         currentgraph = FindGraph(1);
     }
     return 0;