The calculation of required extension used in HBD case was wrong due
to rounding for UV when y dimension is odd. This commit replace the
computation with correct version.
This fixes a crash caused by writting beyond buffer boundary.
Change-Id: Ic7c9afeb7388cd1341ec4974a611dacfb74ac6b6
(cherry picked from commit 4bca73b609bfe9a5cb86fc25b69c6128d9041504)