branches/5.1:

Check whether *trx->mysql_query_str is != NULL in addition to
trx->mysql_query_str. This adds more safety.

This may or may not fix Bug#35226 RBR event crashes slave.

row/row0sel.c

@@ -3577,7 +3577,9 @@ row_search_for_mysql(
 
 	if (trx->isolation_level <= TRX_ISO_READ_COMMITTED
 	    && prebuilt->select_lock_type != LOCK_NONE
-	    && trx->mysql_query_str && trx->mysql_thd) {
+	    && trx->mysql_query_str != NULL
+	    && *trx->mysql_query_str != NULL
+	    && trx->mysql_thd != NULL) {
 
 		/* Scan the MySQL query string; check if SELECT is the first
 		word there */