MDEV-26456: SIGSEGV in flush_tables_with_read_lock on FLUSH TABLE

It is legal that open table can leave unopened tables in SP and other
parts of the code shoud expect it.

mysql-test/main/view.result

@@ -6920,5 +6920,20 @@ Drop View v3;
 Drop View v4;
 Drop table t1;
 #
+# MDEV-26456: SIGSEGV in flush_tables_with_read_lock on FLUSH TABLE
+#
+CREATE FUNCTION f() RETURNS INT RETURN (SELECT 1 FROM t);
+CREATE VIEW v AS SELECT f();
+SELECT * FROM v;
+ERROR HY000: View 'test.v' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them
+FLUSH TABLE v WITH READ LOCK;
+UNLOCK TABLES;
+FLUSH TABLES v FOR EXPORT;
+UNLOCK TABLES;
+SELECT * FROM v;
+ERROR HY000: View 'test.v' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them
+DROP VIEW v;
+DROP FUNCTION f;
+#
 # End of 10.6 tests
 #

mysql-test/main/view.test

@@ -6653,6 +6653,24 @@ Drop View v3;
 Drop View v4;
 Drop table t1;
 
+--echo #
+--echo # MDEV-26456: SIGSEGV in flush_tables_with_read_lock on FLUSH TABLE
+--echo #
+
+CREATE FUNCTION f() RETURNS INT RETURN (SELECT 1 FROM t);
+CREATE VIEW v AS SELECT f();
+--error ER_VIEW_INVALID
+SELECT * FROM v;
+FLUSH TABLE v WITH READ LOCK;
+UNLOCK TABLES;
+FLUSH TABLES v FOR EXPORT;
+UNLOCK TABLES;
+--error ER_VIEW_INVALID
+SELECT * FROM v;
+
+DROP VIEW v;
+DROP FUNCTION f;
+
 --echo #
 --echo # End of 10.6 tests
 --echo #

sql/sql_reload.cc

@@ -601,6 +601,7 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables)
       if (table_list->is_view_or_derived())
         continue;
       if (thd->lex->type & REFRESH_FOR_EXPORT &&
+          table_list->table &&
           !(table_list->table->file->ha_table_flags() & HA_CAN_EXPORT))
       {
         my_error(ER_ILLEGAL_HA, MYF(0),table_list->table->file->table_type(),
@@ -608,6 +609,7 @@ bool flush_tables_with_read_lock(THD *thd, TABLE_LIST *all_tables)
         goto error_reset_bits;
       }
       if (thd->lex->type & REFRESH_READ_LOCK &&
+          table_list->table &&
           table_list->table->file->extra(HA_EXTRA_FLUSH))
         goto error_reset_bits;
     }