Fix loopfilter of leftmost 4x4 edges in SB

For cases where there's no transform set in bit 0 (the left edge of
the SB) but bit 0 of mask_4x4_int is set (the edge 4 pixels from the
left edge needs filtering), it was incorrectly being skipped before.
This situation only happens on the leftmost edge of the image, as
the edge at column 0 is intentionally skipped since there aren't
pixels to the left to read.

Change-Id: Ib2fbbcb40166e90af31b1a0e13b85b68c226cbd3