Add extra check to keep images proportionally scaling by default
from affecting interactive crop preview rectangle.

Change-Id: I2b15bbc8628934e3d3cf17927885ede890505cd3
Reviewed-on: https://gerrit.libreoffice.org/15505Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Yousuf Philips <philipz85@hotmail.com>