The predicate is re-written from
((`test`.`g1`.`a` = geometryfromtext('')) or ...
to
((`test`.`g1`.`a` = <cache>(geometryfromtext(''))) or ...

The range optimizer calls save_in_field_no_warnings, in order to fetch keys.
save_in_field_no_warnings returns 0 because of the cache wrapper,
and get_mm_leaf() proceeded to call Field_blob::get_key_image() 
which accesses un-initialized data.




mysql-test/r/gis.result:
  New test case.
mysql-test/t/gis.test:
  New test case.
sql/item.cc:
  If we have cached a null_value, then verify that the Field can accept it.