maple_tree: Revise limit checks in mas_empty_area{_rev}()

maple_tree: Revise limit checks in mas_empty_area{_rev}()

Since the maple tree is inclusive in range, ensure that a range of 1
(min = max) works for searching for a gap in either direction, and make
sure the size is at least 1 but not larger than the delta between min
and max.

This commit also updates the testing.  Unfortunately there isn't a way
to safely update the tests and code without a test failure.

Suggested-by: Peng Zhang <zhangpeng.00@bytedance.com>
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>