winsys/radeon: check null in radeon_cs_create_fence

Fixes the following segmentation fault:

radeon_drm_cs_add_buffer (bo=0x0) at radeon_drm_cs.c
  -> if (!bo->handle)
(gdb) bt
0  radeon_drm_cs_add_buffer (bo=0x0) at radeon_drm_cs.c
1  0x00007fffe73575de in radeon_cs_create_fence radeon_drm_cs.c
2  0x00007fffe7358c48 in radeon_drm_cs_flush radeon_drm_cs.c

Signed-off-by: Julien Isorce <jisorce@oblong.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit d09edb01468ca385b6a8ffe29ac434dc42a78d07)
Nominated-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed