Use GameObjectType to check the ./fill target

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/engine/devcmd/cmds/FillCmd.java

@@ -56,7 +56,7 @@ public class FillCmd extends AbstractDevCmd {
             }
         }
 
-        if (!(target instanceof Building)) {
+        if (target == null || target.getObjectType() != mbEnums.GameObjectType.Building) {
             throwbackError(pc, "Select a warehouse");
             return;
         }