Item_func_spatial_collection::fix_length_and_dec()
changed to use argument's print() method to print
the ER_ILLEGAL_VALUE_FOR_TYPE error.


mysql-test/r/gis.result:
  Fix for bug#56679: gis.test: valgrind error
    - test result adjusted.
sql/item_geofunc.h:
  Fix for bug#56679: gis.test: valgrind error
    - use argument's print() method instead of improper val_str()
  call in the Item_func_spatial_collection::fix_length_and_dec(), as
  it's applicable only for constant items.