This makes the imagebox widget refuse images which have a zero or negative width
or height. A zero size causes problems where a division by zero results in inf
which makes various stuff fail in weird ways later on.
Additionally, cairo's "error surfaces" have a negative size. Displaying those
would cause all sorts of weird problems, too, so we better reject those.
Signed-off-by: Uli Schlachter <psychon@znc.in>
Uli Schlachter