MDEV-4235: Galera: Assertion `0' fails in tdc_remove_table on creating a trigger

Analysis: There is two different THD's using the same table.

Fix: In galera brute force (BF) exclusive locks are cancelled. Thus other threads
could access the same table. Added additional check if this is the case, then we
should not assert here.

sql/sql_base.cc

@@ -9457,10 +9457,22 @@ void tdc_remove_table(THD *thd, enum_tdc_remove_table_type remove_type,
       {
         I_P_List_iterator<TABLE, TABLE_share> it2(share->used_tables);
         while ((table= it2++))
-          if (table->in_use != thd)
-          {
-            DBUG_ASSERT(0);
-          }
+#ifdef WITH_WSREP
+                /* if thd was BF aborted, exclusive locks were canceled,
+                thus others can use table */
+
+                if (table->in_use != thd &&
+                    table->in_use->wsrep_bf_thd != thd &&
+                    table->in_use->wsrep_conflict_state != MUST_ABORT)
+                {
+#endif
+                  if (table->in_use != thd)
+                  {
+                      DBUG_ASSERT(0);
+                  }
+#ifdef WITH_WSREP
+                }
+#endif
       }
 #endif
       /*