MDEV-18286 Assertion `pagecache->cnt_for_resize_op ...

This patch is also pushed in 10.4. It's pushed separately in 10.5 as there
are some additional cases in 10.5 to take care of.

When merging if there is conflicts, use this code, not the 10.4 code.

storage/maria/ma_pagecache.c

@@ -3710,6 +3710,7 @@ uchar *pagecache_read(PAGECACHE *pagecache,
         {
           /* block is unregistered in read_big_block */
           pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
+          dec_counter_for_resize_op(pagecache);
           DBUG_PRINT("restart", ("big block fail, restarting..."));
           goto restart;
         }
@@ -3754,6 +3755,7 @@ uchar *pagecache_read(PAGECACHE *pagecache,
         unreg_request(pagecache, block, 1);
       dec_counter_for_resize_op(pagecache);
       pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
+      dec_counter_for_resize_op(pagecache);
       DBUG_PRINT("info", ("restarting..."));
       goto restart;
     }
@@ -4176,6 +4178,7 @@ my_bool pagecache_delete(PAGECACHE *pagecache,
         unreg_request(pagecache, block, 1);
       dec_counter_for_resize_op(pagecache);
       pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
+      dec_counter_for_resize_op(pagecache);
       DBUG_PRINT("info", ("restarting..."));
       goto restart;
     }