Fix no resizing for initial size

If container is 100% window's width and I reduce the window's size, when
I maximize the window to it's initial size, filling was not working.
Merge branch 'fix-resize-to-initial' of https://github.com/In4matik/imagefill.js into In4matik-fix-resize-to-initial
Merge branch 'In4matik-fix-resize-to-initial'