fix avatar manipulation when selecting an image

The crop area was not being set correctly when selecting an image
from a file. Also the crop area needs to be re-set (re-initialized)
each time a new image is used because otherwise it behaves weirdly
if the new image is smaller than the previous.

Change-Id: Ieef9b3f537567f3823dbd9f4cb18667c80d740c7
Tuleap: #917