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
Change-Id: Id0d6094da796ca67338d8ad225fa6b2f309bbe6e
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>