Blender Git Loki

Fix a bug in the T34039 hack in case when a modifier key is not mapped.

In order to recover from a transient Focus Out - Focus In disruption
in the middle of a shortcut, which can be caused by certain window
managers, Blender has code that checks which modifier keys are pressed
after Focus In and restores the modifier state based on that.

If one of the Ctrl, Shift, Alt, Super keys is not mapped anywhere
in the active keyboard layout, XKeysymToKeycode returns the invalid
zero keycode, and reading the key state produces garbage, which can
cause an invalid modifier state. Check the return value to avoid this.