core: Apply the same treatment to the in errno message in __igt_fail_assert()

Just like the it was done for the requirement message, display the errno
message only if errno is set, and display it at the end of the assert
message.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
1 file changed