Fixed #659

Fixes #659

This will fix the sounds not playing when paused. The issue was due to the interface between the original and the new sounds mixer. When paused the currently playing sound would get deleted but not marked as finished due to the update logic being in game_logic_update instead of game_update. I've labeled the offset for the max number of concurrent sounds so someone could probably bring 0x009AF604 (3 byte table) into openrct2. This also means that we now know partially what sound quality in the options does. 

I've also put in a little protection against dereferencing a null widget when there is a mouse input. This was causing issues when testing the sound and it might be a sign that something is misbehaving although I couldn't find a cause. Possibly just a race condition that can only happen when stepping through code.