Guild PQ + fixed negative EXP error

Implemented Guild PQ. Fixed a problem introduced earlier where negative
EXP would be deemed as "integer overflow", provoking many game breaking
issues as result.

src/scripting/npc/NPCScriptManager.java

@@ -118,6 +118,7 @@ public class NPCScriptManager extends AbstractScriptManager {
     public void dispose(NPCConversationManager cm) {
         MapleClient c = cm.getClient();
         c.getPlayer().setCS(false);
+        c.getPlayer().setNpcCooldown(System.currentTimeMillis());
         cms.remove(c);
         scripts.remove(c);