xfree86: Move secondary GPU autoconfig loop break
Commit d458f84e (xfree86: Fix autoconfig secondary GPU devices) introduced a potential segmentation fault when all GPU devices were assigned to a different seat than the one being configured. This commit fixes that bug by moving the break on NULL before the code which causes the crash. The other potential fix for this bug is to leave the break where it is and add a check for NULL in the if block to ensure that all NULLs end up in the if case. That fix maintains the invariant that the conf_screen->screen_gpu_devices list ends with NULL while the one in this commit does not. Inspection of the code reveals that the code does not depend on that invariant. Since moving the break is both simpler and more proper than the other fix, it is the fix chosen for this commit. Signed-off-by: Jacob Cherry <jcherry@nvidia.com>