Fix Half Pel MC on Last Ref Row

If MC is referring to the last MB row, in case of field pictures,
it could incorrectly read up to 8 extra rows in the reference
buffer and 9 rows in case of half_y prediction.

Bug: 63873837
Test: ran POC on patched ASAN-enabled code
Change-Id: I83af03b3c6b7e08a984f7b383bedf706422f6354
1 file changed