This is the MariaDB 10.2 version of the patch.

field_store_string(): Simplify the code.

field_store_index_name(): Remove, and use field_store_string()
instead. Starting with MariaDB 10.2.2, there is the predicate
dict_index_t::is_committed(), and dict_index_t::name never
contains the magic byte 0xff.

Correct some comments to refer to TEMP_INDEX_PREFIX_STR.

i_s_cmp_per_index_fill_low(): Use the appropriate value NULL to
identify that an index was not found. Check that storing each
column value succeeded.

i_s_innodb_buffer_page_fill(), i_s_innodb_buf_page_lru_fill():
Only invoke Field::set_notnull() if the index was found.
(This fixes the bug.)

i_s_dict_fill_sys_indexes(): Adjust the index->name that was
directly loaded from SYS_INDEXES.NAME (which can start with
the 0xff byte). This was the only function that depended
on the translation in field_store_index_name().