[MSPAINT] Fix scrollbar presence on canvas/view fitting

This is a small fix for a scrollbar related edge case functionality exhibited in mspaint (and in a lesser degree also elsewhere in instances of) scrollbar controlled content. As known, the scrollbars presence is given by the size ratio between the accommodating outer frame and the scroll-controlled contents inside it, and it works for the most part. There is, however, a case where the presence of both toolbars is kept even when the contents would fit the frame (if not for the scrollbars themselves that increase the size of the contents' area).

https://github.com/reactos/reactos/pull/878