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: cec0bc73 ("turnip: rework fences to use syncobjs") Signed-off-by: Vinson Lee vlee@freedesktop.org
cc: @flto