Fixed the strange bug kelly reported. I really thought we already had proper checks for the resolution values but it turned out that NaN is greater than GIMP_MIN_RESOLUTION (which is 1e-5 at the moment).
Eventually I'll rise the GIMP_MIN_RESOLUTION value to something that gets displayed as != 0 in the UI with the number of digits we supply for our units. Actually that would mean setting it to 1e-3. Will that be small enough? In the past each time we set a limit someone immidiately started to complain...
