We didn't implement an empty geometry. And returning NULL instead of it is not
    quite correct. So here is the implementation of the empty value as GEOMETRYCOLLECTION().

per-file comments:
  mysql-test/r/gis-precise.result
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    test result updated.

  mysql-test/r/gis.result
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    test result updated.

  mysql-test/t/gis-precise.test
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    test case added.

  mysql-test/t/gis.test
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    test case added.

  sql/field.cc
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    store GEOMETRYCOLLECTION() properly.

  sql/gcalc_tools.cc
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    create the GEOMETRYCOLLECTION() for the empty result.

  sql/gstream.h
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    next_symbol() added.

  sql/spatial.cc
bug 801466 ST_INTERSECTION() returns invalid value on empty intersection in maria-5.3-gis.
    code modified to handle 0 geometries in the GEOMETRYCOLLECTION properly.