Fix an off-by-one error in setting the "iLevel" field of the
sqlite3_rtree_query_info structure passed into the RTree query callback.
Be sure to initialize the sqlite3_rtree_query_info.iRowid field for the
leaves of the R-Tree when doing a query callback search.
Fix the generation of sqlite3_rtree_query_info.iRowid and add test cases
to verify that it is fixed.