#388 Do not activate Menu Bar when pressing Alt

[ingwer]

this feature introduced an issue:
[#384]: Alt and Shift can be used in combination with the mouse wheel to trigger horizontal scrolling in the timeline.

After pressing alt + mouse wheel up/down to trigger horizontal scrolling the menu bar is activated by alt key. Hence when pressing Space after scrolling via alt + mouse wheel, to start the playback the title bar menu is shown instead of executing the playback. Do no activate the menu bar when pressing alt to avoid this.