Prior to the implementaiton of raw mouse input, a low-level mouse hook was used for capturing mouse events. Windows would emit a single WM_* event per button state change. With the move to capturing raw mouse input events, it was expected that this behavior remained, despite now needing to listen for WM_INPUT events.

However, unlike when using the low-level hook, WM_INPUT events can contain data for multiple simultaneous mouse state changes. If this occurred, Mumble would register none of the state changes.

Changing the logic to account for multiple state changes in a single event correctly allows for all states changes to be registered.

Fixes mumble-voip#5706

(cherry picked from commit 01af7d9)