Bug #46495 Crash in reload_acl_and_cache on SIGHUP

      
An assert in reload_acl_and_cache didn't account for the
case when the function is called with a NULL thd.  A
null thd is used whenever the function is called from the
SIGHUP signal handler.

Backported from 6.0-codebase  (revid: 2617.69.35)

sql/sql_parse.cc

@@ -6568,7 +6568,7 @@ bool reload_acl_and_cache(THD *thd, ulong options, TABLE_LIST *tables,
   }
 #endif /*HAVE_QUERY_CACHE*/
 
-  DBUG_ASSERT(thd->locked_tables_mode || !thd->mdl_context.has_locks());
+  DBUG_ASSERT(!thd || thd->locked_tables_mode || !thd->mdl_context.has_locks());
 
   /*
     Note that if REFRESH_READ_LOCK bit is set then REFRESH_TABLES is set too