Coordinates of right image border

[ChristPi]

When labeling a 640x480 image the coordinates possible for bounding boxes are 0 to 480 in vertical direction and 0 to 641 in horizontal direction. It seems to be impossible to get exactly the coordinate 640.
When saving a label with the coordinate 641, editing the label will result in editing a replacement 2x2 box.

[NFiedler]

I think the problem is a result of a rounding error. We should set those values to min(0) and max(width or height -1)after drawing them into the image.

[ChristPi]

Trying to edit an old image with a coordinate of 640 will result in a similar scenario of a replacement 2x2 box. Editing a box at any other of the edges will not result in this bug