Fixed potential access violation in QPixmap::copy() for <32 bit pixmaps.

QImage is supposed to maintain the invariant that each scan-line begins
on a 4-byte boundary, so we need to verify that this is the case before
using the optimized path of short-cutting QImage::copy() by referencing
the source image's bits directly.

Task-number: QTBUG-14766
Change-Id: I0a178aeb2f34cc64f98deae9470b55b5c53fcb06
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
(cherry picked from commit 711773776ed324efce7f1ed227104da9c7e21e05)
Reviewed-by: aavit <eirik.aavitsland@digia.com>
Fixed invalid memory read in SSSE3 image blending code.

We need to do bounds comparison on the actual offset we're going to use
with _mm_load_si128 to read 16 bytes from memory (even though we won't
use the trailing bytes in the end).

Task-number: QTBUG-28324
(cherry-picked from qtbase commit 52619ae7787b3c4febb73a02afa623b12edabc97)
Change-Id: I705ae191312e5ffe25e45caea71ada73ec97f68d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>