Fix PianoRoll changing editMode outside window

If an user Ctrl+Clicked on a track, e.g. copying/muting it, but the
focus was still on the PianoRoll window the mode would change

Fix #1501 

Please bear in mind that this can be one of a class of bugs related to the keyPress event being triggered outside of the window without being keyReleased, this is a very simple fix for this specific case. A different `FocusPolicy` or a check in the beggining of this function may be better solutions.