Internal caclucations can't handle zero distance properly.
        As the ST_BUFFER(geom, 0) is in fact NOOP, we'll just return the
        'geom' as the result here.

per-file comments:
  mysql-test/r/gis-precise.result
fix for bug #201189 ST_BUFFER asserts if radius = 0.
        test result updated.

  mysql-test/t/gis-precise.test
fix for bug #201189 ST_BUFFER asserts if radius = 0.
        test case added.

  sql/item_geofunc.cc
fix for bug #201189 ST_BUFFER asserts if radius = 0.
        return the first argument as the result of the ST_BUFFER, if
        the distance is 0 there.