When chat scrolls, IDBearer URL menus shouldn't lead to the wrong place

Optimizes away multiple iterations over scroll lists and
multiple parsings of urls to determine the target(s)
At the cost of the last selection being stored statically in a vector

Removes virtual LFIDBearer::getNumSelected

indra/newview/llnetmap.h

@@ -70,7 +70,6 @@ public:
 
 	LLUUID getStringUUIDSelectedItem() const override final { return mClosestAgentAtLastRightClick; }
 	uuid_vec_t getSelectedIDs() const override final { return mClosestAgentsAtLastClick; }
-	S32 getNumSelected() const override final { return mClosestAgentsAtLastClick.size(); }
 
 // [SL:KB] - Patch: World-MinimapOverlay | Checked: 2012-06-20 (Catznip-3.3.0)
 	void			refreshParcelOverlay() { mUpdateParcelImage = true; }