wsi/x11: Fix possible null pointer deference
Fix defect CID-1476002 reported by Coverity Scan.
wsi_x11_get_connection() could return NULL in case of memory allocation failure. Added 'if' to catch this case, as it is done in all other usages of this function.
Fixes:
Signed-off-by: Yevhenii Kharchenko yevhenii.kharchenko@globallogic.com