SkScaledBitmapSampler: fix memory overwritten

Cherry-picked from https://codereview.chromium.org/1085253002
in Skia.

Memory will be overwritten while downsampling some
interlaced gif images, most commonly with odd sizes,
when index of destination row stores in the current
line computed from GifInterlaceIter meets:

 X is an integer in [0..height-1]
   and
 (X < height)
 && ((X - sampleSize/2) % sampleSize == 0)
 && ((X - sampleSize/2)/sampleSize >= height/sampleSize)

Signed-off-by: Lu Tong <lu.x.tong@sonymobile.com>

BUG=skia:

Review URL: https://codereview.chromium.org/1085253002

BUG:20723696
Change-Id: I2cca83a2a5c39b5a497f36b40724262b438ead8b
1 file changed