Spawn monsters without prematurely exiting. Fixes BUKKIT-3425

By using return 0, we exit the loop prematurely preventing other
creature types from being spawned if one type is set to 0. By using
continue we move on to the other types and allow them to spawn
properly.

src/main/java/net/minecraft/server/SpawnerCreature.java

@@ -86,7 +86,7 @@ public final class SpawnerCreature {
                 }
 
                 if (limit == 0) {
-                    return 0;
+                    continue;
                 }
                 // CraftBukkit end