BUG#41980 SBL, INSERT .. SELECT .. LIMIT = ERROR, even when @@SQL_LOG_BIN is 0 !

When binlog_format is STATEMENT and the statement is unsafe before,
the unsafe warning/error message was issued without checking
whether the SQL_LOG_BIN was turned on or not.
      
Fixed with adding a sql_log_bin_toplevel flag in THD to check
whether SQL_LOG_BIN is ON in current session whatever the current is in sp or not.

sql/sql_class.h

@@ -1350,6 +1350,8 @@ public:
 
   /* <> 0 if we are inside of trigger or stored function. */
   uint in_sub_stmt;
+  /* TRUE when the current top has SQL_LOG_BIN ON */
+  bool sql_log_bin_toplevel;
 
   /* container for handler's private per-connection data */
   Ha_data ha_data[MAX_HA];