exrdisplay: limit maximum image size based on available screen res

[peterhillman]

As discussed in #610 , exrdisplay doesn't handle large images well. It will always try to match the window resolution to the image size. It doesn't have the ability to resize the window, zoom out, or pan around an image, making it impractical to use with images that are larger than the screen size. Very large images may create windows which are too large for window managers, and exrdisplay will allocate excessive amounts of memory to load them.

This change simply aborts loading early with images that are more than twice as wide or high as the screen.

Signed-off-by: Peter Hillman peterh@wetafx.co.nz

[cary-ilm]

This seems reasonable to me. As you say, exrdisplay isn't intended as a full-featured image viewer, it primarily functions as example code. This plugs what could be construed as a vulnerability.