MDEV-19263: Server crashes in mysql_handle_single_derived upon 2nd execution of PS

Fix case of prelocking placeholder

mysql-test/main/ps.result

@@ -5388,3 +5388,21 @@ drop table t1;
 #
 # End of 10.2 tests
 #
+#
+# MDEV-19263: Server crashes in mysql_handle_single_derived
+# upon 2nd execution of PS
+#
+CREATE TABLE t1 (f INT);
+CREATE VIEW v1 AS SELECT * FROM t1;
+CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW INSERT INTO v1 SELECT * FROM x;
+PREPARE stmt FROM "INSERT INTO v1 VALUES (1)";
+EXECUTE stmt;
+ERROR 42S02: Table 'test.x' doesn't exist
+EXECUTE stmt;
+ERROR 42S02: Table 'test.x' doesn't exist
+DEALLOCATE PREPARE stmt;
+DROP VIEW v1;
+DROP TABLE t1;
+#
+# End of 10.4 tests
+#

mysql-test/main/ps.test

@@ -4825,3 +4825,27 @@ drop table t1;
 --echo #
 --echo # End of 10.2 tests
 --echo #
+
+--echo #
+--echo # MDEV-19263: Server crashes in mysql_handle_single_derived
+--echo # upon 2nd execution of PS
+--echo #
+
+CREATE TABLE t1 (f INT);
+CREATE VIEW v1 AS SELECT * FROM t1;
+CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW INSERT INTO v1 SELECT * FROM x;
+PREPARE stmt FROM "INSERT INTO v1 VALUES (1)";
+
+--error ER_NO_SUCH_TABLE
+EXECUTE stmt;
+--error ER_NO_SUCH_TABLE
+EXECUTE stmt;
+
+# Cleanup
+DEALLOCATE PREPARE stmt;
+DROP VIEW v1;
+DROP TABLE t1;
+
+--echo #
+--echo # End of 10.4 tests
+--echo #

sql/sql_derived.cc

@@ -183,7 +183,10 @@ mysql_handle_single_derived(LEX *lex, TABLE_LIST *derived, uint phases)
   if (!lex->derived_tables)
     DBUG_RETURN(FALSE);
 
-  derived->select_lex->changed_elements|= TOUCHED_SEL_DERIVED;
+  if (derived->select_lex)
+    derived->select_lex->changed_elements|= TOUCHED_SEL_DERIVED;
+  else
+    DBUG_ASSERT(derived->prelocking_placeholder);
   lex->thd->derived_tables_processing= TRUE;
 
   for (uint phase= 0; phase < DT_PHASES; phase++)