x11: try to fix crash in xkb_x11_keymap_new_from_device error handling

x11: try to fix crash in xkb_x11_keymap_new_from_device error handling

In 1b3a1c277a033083fee669e92c8cad862716ebd1 we changed the error
handling in this code to not bail out immediately but only after
everything has been processed, to simplify the code. But I suspect the
code isn't prepared for this and that's what causing the crash reported
in the issue.

Bring back the short-circuit error handling which would hopefully fix
such crashes.

Fixes: https://github.com/xkbcommon/libxkbcommon/issues/252
Signed-off-by: Ran Benita <ran@unusedvar.com>