Small bug-fixes: Item dragging & npc interactions.

Fixed a series of rather small bugs involving item dragging and vendors windows:

- Fixed a bug allowing players to "drag" vendor items across map loads.
- Fixed a bug caused by eventPendingDialog not being properly initialized, it was possible to interact with an NPC out of range when first loading the game
- Fixed a bug which left the vendor window open despite your avatar being out of max_interact_range when the player was dragging an item