If multiple threads invoke buf_page_get_low() on a ROW_FORMAT=COMPRESSED
page that does not reside in the buffer pool, then one of the threads
will end up acquiring an exclusive page latch (the "if" statement
right before the new wait_for_unzip: label) and other threads will
end up waiting for a shared latch while holding a buffer-fix.
The exclusive latch holder would then wait for the buffer-fixes to
be released while the buffer-fix holders are waiting for the shared latch.

buf_page_get_low(): Prevent the hang that was introduced
in commit 9436c778 (MDEV-27058),
by releasing the buffer-fix, sleeping some time, and retrying the
page lookup.