Revert to the user's chosen resolution, not to 0x0, which would then be
coerced to the minimum resolution. When the text says revert, it should
revert, not just pick a size.
Change the "OK" label to say "Revert to NxM" for the resolution it is
reverting to.
Tighten input validation so that a blank width or blank height produce
the correct error message, rather than being coerced to 0, then
rejecting 0 as too small.