Screen rotation in fullscreen mode causes pictures to be drawn in tile pattern

[finnteegen]

When you start feh in fullscreen mode and perform a screen rotation while running a slideshow, pictures are drawn in a tile pattern. I think this is due to the pixmap not being adjusted properly. As a quickfix (see finnteegen/feh@74141ec), I set the pixmap's dimensions in fullscreen mode to the maximum of the screen's width and height. While this does fix the issue, I am not sure if this is the best way to do so.