Problem: in case of wrong data insert into indexed GEOMETRY fields 
(e.g. NULL value for a not NULL field) MyISAM reported 
"ERROR 126 (HY000): Incorrect key file for table; try to repair it"
due to misuse of the key deletion function.

Fix: always use R-tree key functions for R-tree based indexes
and B-tree key functions for B-tree based indexes.


mysql-test/r/gis-rtree.result:
  Bug#11764487: myisam corruption with insert ignore and invalid spatial data
    - test result.
mysql-test/t/gis-rtree.test:
  Bug#11764487: myisam corruption with insert ignore and invalid spatial data
    - test case.
storage/myisam/mi_update.c:
  Bug#11764487: myisam corruption with insert ignore and invalid spatial data
    - handling update errors check for HA_ERR_NULL_IN_SPATIAL as well to be 
  consistent with mi_write();
    - always use keyinfo->ck_delete()/ck_insert() instead of _mi_ck_delete()/_mi_ck_write()
  to handle index properly, as it may be of B-tree or R-tree type.
storage/myisam/mi_write.c:
  Bug#11764487: myisam corruption with insert ignore and invalid spatial data
    - always use keyinfo->ck_delete() instead of _mi_ck_delete() to handle
  index properly, as it may be of B-tree or R-tree type.