Minor fix about jpeg downscale under max texture size

Let we consider that two cases also downscale works well when
 - Mark as we don't use jpeg scale factor, and double-scaled image size is less then max texture size.
   (For this case, we were try to decode image as double-scaled. and then downscale as half)
 - 1/8 scaled size of image is also less then max texture size
   (For this case, we should try to downscale as much as we can. But we didn't)

Change-Id: I861e40c8e01872e133bcee90f13466effaa83f47
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>