turnip: Close sync_fd only if it is a valid file descriptor.

Fix defects reported by Coverity Scan.

Argument cannot be negative (NEGATIVE_RETURNS)
negative_returns: sync_fd is passed to a parameter that cannot be negative.

Fixes: cec0bc73e55 ("turnip: rework fences to use syncobjs")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7647>
(cherry picked from commit 69cad1f96ef4481cc2395def9c993ddcbb0e2540)
2 files changed