MDEV-23134 SEGV in dict_load_table_one during restart after server crash

Problem:
========
dict_load_table_one() doesn't handle the scenario where clustered
index page is FIL_NULL when DICT_ERR_IGNORE_INDEX_ROOT mode
is set.

Fix:
====
InnoDB should set the file_unreadable when it can't find the
clustered index root page.

storage/innobase/dict/dict0dict.cc

@@ -5804,6 +5804,7 @@ dict_set_corrupted_index_cache_only(
 	is corrupted */
 	if (dict_index_is_clust(index)) {
 		index->table->corrupted = TRUE;
+		index->table->file_unreadable = true;
 	}
 
 	index->type |= DICT_CORRUPT;