The shortest direction calculation used integer math to determine
which direction to move.  For an odd modelCount, the wrong direction
could be chosen.  For a modelCount of 1 it was particularly obvious.

Task-number: QTBUG-21337
Change-Id: I5e75c74153a5b4c62d1536226cd0703dcae04178
Reviewed-by: Andrew den Exter <andrew.den-exter@nokia.com>