LP:603654 - Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' with virtual columns

When a virtual column is used in an ORDER BY, the server asserts as follows:

mysqld: field.cc:6610: virtual String* Field_string::val_str(String*, String*): Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed.

This is not observed if the expression from the virtual column is inlined in the query, so it seems to be a virtual-columns-specific bug.