Check that QSHotKeyEditor is the first responder before handling modifiers

Fixes a problem I discovered while trying to rename an ugly-named default Trigger in the Trigger Info pane. Hotkey input would get redirected to the wrong text field, preventing me from typing anything useful.

Please note : this looks like a complete hack, but then I have the feeling the entire contents of that file is a hack (since the first responder mechanism *should* actually prevent that).