Problem: involving a spatial index for "non-spatial" queries
(that don't containt MBRXXX() functions) may lead to failed assert.

Fix: don't use spatial indexes in such cases.


mysql-test/r/gis-rtree.result:
  Fix for bug#48258: Assertion failed when using a spatial index
    - test result.
mysql-test/t/gis-rtree.test:
  Fix for bug#48258: Assertion failed when using a spatial index
    - test case.
sql/opt_range.cc:
  Fix for bug#48258: Assertion failed when using a spatial index
    - allow only spatial functions (MBRXXX) for itMBR keyparts.