Do not segfault just because an error has not been given

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Try to use DISPLAY=:0 if not in X

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Fix #64: Fix Geoclue support when run outside of X

Fix check of error value returned.
Geoclue requires DISPLAY to be set, so try DISPLAY=:0 if not already set.