input: fallback for keymap compilation failure
If in weston.ini has an invalid keyboard layout, the xkb keymap compilation fails, and the Weston clients can't use their keyboard layout, resulting in a crash when try to type.
Fallback to XKB defaults to avoid the crash.
Issue: #177 (closed)
Signed-off-by: Silva Alejandro Ismael silva.alejandro.ismael@gmail.com