Should be possible to sample a pixel at the maximum of a sampler

Hi all,
I think this fixes the following bug in the latest build:

* Open ImageJ
* File/Open Samples/Clown
* Image/Duplicate

Nothing happens (except the log shows a null pointer exception). The proximate cause, however, is another exception that's thrown because the SamplingDefinition falsely reports that a constraint can't include the realMax of the sampler, but you can sample *at* the realMax of a sampler.

This patch fixes the bug, hope I understood correctly and it doesn't break something else.

--Lee