#190 Don't change dimension presets after cropping a page

[Michael von Glasow]

After each crop operation the width selection in the dialog gets reduced by the X offset.

Example: Choose X offset = 100 px, width = 1337 px and crop one page. The page will be cropped correctly but after that the dialog will suggest a width of 1237 px. (Same probably goes for height but I haven't tested that.)

This is annoying when cropping multiple pages to the same size (but with different offsets) – a common occurrence when editing scans where the original was not aligned properly.

This may be because with the new page size the settings made before would exceed the page dimensions (you can't cut 100 px off a page that is 1337 px wide and still have a page 1337 px in width).

A solution would be not to enforce page dimensions immediately after cropping. Maybe allow values exceeding page dimensions to be entered and report an error only when the user clicks Crop – then offer to correct the values so they'll fit onto the page.