MDEV-18286 Assertion `pagecache->cnt_for_resize_op == 0' failed in
check_pagecache_is_cleaned_up on server shutdown

The reason for the crash is that the counter-of-pinned-pages in the
Aria pagecache goes wrong.
This only affects debug builds, as in these we do an assert on shutdown
if the counter-of-pinned-pages is not 0 (some page was left pinned).

The bug was that in 2 places in the page cache, when not succeeding to
pin a page and a retry was made, the counter-of-pinned-pages counter was
not properly adjusted.

In the given test case, BLOCK_COMMIT flushed all Aria files. If a block was flushed at the same time the insert tried to access it, the insert would retry to get the block and that would cause the counter to go wrong.