Don't crash if there are no ibus keyboards installed (FWNX-1382)

If IBus is running but there are no ibus input methods listed in
the IBus Preferences we shouldn't try to set an ibus keyboard. This
might actually fix FWNX-1382.

Change-Id: I0e9fc9dc8344bc75aa281b7bb8994a2af9c958ee
Merge pull request #23 from ermshiperete/feature/FWNX-1382

Don't crash if there are no ibus keyboards installed (FWNX-1382)