When specifying a RANGE type frame that exceeds the partition size, both
for the top and bottom cursors we end up removing more rows than added
to the aggregate function. This happens because our TOP range cursor,
which removes values from the aggregate function, would be allowed to breach
partition boundaries, while the BOTTOM range cursor would not.

To prevent this from happening, force the TOP range cursor to only move
within the current partition, as does the BOTTOM range cursor.