MDEV-37360: SIGSEGV in srv_printf_innodb_monitor

srv_printf_innodb_monitor(): After acquiring a latch,
abort the iteration if innodb_adaptive_hash_index=OFF.
If the adaptive hash index was disabled in a concurrently
executing thread, btr_search_sys_t::partition::clear() would have
freed part->heap, leading to us dereferencing a null pointer.

Reviewed by: Thirunarayanan Balathandayuthapani
Tested by: Saahil Alam

Author: dr-m

storage/innobase/srv/srv0srv.cc

@@ -774,6 +774,10 @@ srv_printf_innodb_monitor(
 		for (ulint i = 0; i < btr_ahi_parts; ++i) {
 			const auto part= &btr_search_sys.parts[i];
 			part->latch.rd_lock(SRW_LOCK_CALL);
+			if (!btr_search_enabled) {
+				part->latch.rd_unlock();
+				break;
+			}
 			ut_ad(part->heap->type == MEM_HEAP_FOR_BTR_SEARCH);
 			fprintf(file, "Hash table size " ULINTPF
 				", node heap has " ULINTPF " buffer(s)\n",