Fix button 2 and 3 when releasing the mouse button on Linux

[TolikPylypchuk]

button_map_lookup - a function which swaps button 2 and 3 - is called twice when dispatching the mouse release event. First time at the very beginning of dispatch_mouse_release, and then another time in the switch statement, which means that buttons 2 and 3 are swapped when dispatching mouse release events on Linux.

This is a problem only on 1.3 - on 1.2 everything looks fine.