Attached Docker does not finish handling the Mouse Wheel

Reaper by default and most users use the Mouse Wheel to Zoom and navigate the Arrange View of the Main window. The Mouse Wheel is handled correctly on any separate window (MIDI Editor, FX Editor, Media Explorer) that is not docked and attached to the Main Window.

However when these windows are Docked and Attached, any Mouse Wheel event that is not fully handled by them leaks out to the Main window and messes up the Arrange View on the side, away from the mouse.

For example, in Media Explorer, if you are adjusting the preview volume slider with the wheel, and inadvertently drift outside the slider by a little, there goes what you are looking at in the Arrange View.

The most prominent workflow problem is when editing FX with the wheel. All JS, Rea--, and all VST effects in non-UI mode suffer from this problem. A little drift while adjusting a JS slider with the wheel, the Mouse Wheel event flows to its UI background unhandled and leaks out to the Main window, and there goes the Arrange view.

Some top VSTs (such as EQuilibrium) extensively use the Mouse Wheel event and do not mark it as handled (and for most hosts they do not need to). Hence editing these with the Mouse Wheel is impossible as it messes up the Arrange view. Even if they mark the event handled for their widget areas, they too suffer from their adjacent background areas messing with the Arrange view.

The fix is for the attached Docker to terminate any leftover Mouse Wheel events and not forward them to the Main window Action handler, just like when in a separate window.