client: Don't handle hotkeys while sticky alt is active

In some cases rhev-m changes the hotkey for releasing the mouse grab
to ctrl + alt. This makes it impossible to send ctrl + alt + other-key
to the guest, even when using sticky alt.

What happens is:
-press alt until sticky alt activates
-release alt (but recorded state stays pressed due to sticky alt)
-press ctrl
-hotkey code sees ctrl+alt pressed, releases mouse grab
-mouse grab release code does an unpress all -> end of sticky state.

This patch makes it possible to atleast send ctrl + alt + del (or other key)
using sticky alt. Note: even with this patch it is still a bad idea to
use ctrl + alt as hotkey combi.