MDEV-23839 innodb_fast_shutdown=0 hang on change buffer merge

ibuf_merge_or_delete_for_page(): Do not attempt to invoke ibuf_delete_recs() on a page of the change buffer itself. The caller could already be holding ibuf->index->lock, and an attempt to acquire it in S mode would hang the release server or cause an assertion failure in rw_lock_s_lock_func() in a debug server. This problem was reproducible on 1 out of 2 runs of the following: ./mtr --no-reorder \ innodb.innodb-page_compression_default \ innodb.innodb-page_compression_snappy \ innodb.innodb-page_compression_zip \ innodb.innodb_wl6326_big innodb.xa_recovery

Author: dr-m

storage/innobase/ibuf/ibuf0ibuf.cc

@@ -4472,7 +4472,10 @@ ibuf_merge_or_delete_for_page(
 
 fil_space_release(space);
 if (UNIV_UNLIKELY(srv_shutdown_state)
- && !srv_fast_shutdown) {
+ && !srv_fast_shutdown
+ && (!block
+|| btr_page_get_index_id(block->frame)
+!= DICT_IBUF_ID_MIN + IBUF_SPACE_ID)) {
 /* Prevent an infinite loop on slow
 shutdown, in case the bitmap bits are
 wrongly clear even though buffered