Bug#13707 - Server crash with INSERT DELAYED on MyISAM table

Initialized 'ptr' for a newly instantiated varstring field.
This is required by INSERT DELAYED.

No test case. This is a migration issue. There are two shell
scripts attached to the bug report. They can be used for testing.

sql/field.cc

@@ -6202,9 +6202,16 @@ Field *Field_string::new_field(MEM_ROOT *root, struct st_table *new_table)
     This is done to ensure that ALTER TABLE will convert old VARCHAR fields
     to now VARCHAR fields.
   */
-  return new Field_varstring(field_length, maybe_null(),
+  Field *new_field= new Field_varstring(field_length, maybe_null(),
                                         field_name, new_table,
                                         charset());
+  /*
+    delayed_insert::get_local_table() needs a ptr copied from old table.
+    This is what other new_field() methods do too. The above method of
+    Field_varstring sets ptr to NULL.
+  */
+  new_field->ptr= ptr;
+  return new_field;
 }
 
 /****************************************************************************