Fix origin and zdone for invalid country argument

Invalid country argument was interpreted as (natid)-1, which is
normally 255.  Harmless as long as this is less than MAXNOC (99).
Wrong anyway.

src/lib/commands/orig.c

@@ -43,7 +43,7 @@ orig(void)
     char *p;
     coord x, y;
     char buf[1024];
-    natid cnum;
+    int cnum;
     struct natstr *np;
 
     p = getstarg(player->argp[1], "New origin (sector or country) : ", buf);

src/lib/commands/zdon.c

@@ -59,7 +59,7 @@
 int
 zdon(void)
 {
-    natid whichcnum;
+    int whichcnum;
     struct natstr *natp;
     char *p;