This is a side-effect of my_large_malloc() introduction,MDEV-18851

It removed a cast to size_t to variable 'blocks' in
multiplication blocks * keycache->key_cache_block_size , creating ulong value
instead of correct size_t.


Replaced a couple of ulongs with appropriate data type, which is size_t.

Also, fixed casts to ulongs in crash handler messages, so that people would
not be confused by that, too.

Interestingly, aria did not expose the same problem even if it contains
copied and pasted code in ma_pagecache, because Aria had some ulongs removed
when fixing a similar problem in MDEV-9256.