DIB: handle images of odd width

[ForNeVeR]

@ForNeVeR I found a bug in Dib.fs. In particular, stride was incorrectly calculated in odd-width bitmaps.

It seems that there are no such sprites in the game files anymore, but if you want to put this in a external library, you will need to check the 1bpp and 8bpp formats for this bug.

Originally posted by @sotiredofyours in https://github.com/ForNeVeR/O21/issues/79#issuecomment-1511758090