optimize LLMuteList::isMuted; Don't check any lists if the users mute list is emoty anyway. Only pay the price if someone is muted.

indra/newview/llmutelist.cpp

@@ -622,6 +622,11 @@ BOOL LLMuteList::saveToFile(const std::string& filename)
 
 BOOL LLMuteList::isMuted(const LLUUID& id, const std::string& name, U32 flags) const
 {
+	// <FS:ND> In case of an empty mutelist, we can exit right away.
+	if( 0 == mMutes.size() )
+		return FALSE;
+	// </FS:ND>
+
 	// for objects, check for muting on their parent prim
 	LLViewerObject* mute_object = get_object_to_mute_from_id(id);
 	LLUUID id_to_check  = (mute_object) ? mute_object->getID() : id;