test/double-poll-crash: Skip this test if the `mmap()` fails
test/double-poll-crash: Skip this test if the `mmap()` fails

This test is very prone to hiting a SIGSEGV signal due to missing error
handling on mmap() calls. This especially often happens when executing
`runtests-parallel`. Let's just skip this test if those calls fail
instead of having a random segfault with no clear resolution.

Signed-off-by: Ammar Faizi <a8266392a329a5c7b5ab982a8996391d75b6438e@gnuweeb.org>
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing