Fix false remainder handling on privacy mask

[MichaIng]

#2403 (comment)

[jmichault]

Is this bug already present after PR #2479, which closed issue #2434 ?

[MichaIng]

Yes, the underlying issue still exist, also the too large last row and column, depending on camera dimensions. I don't find much time at the moment, but let me keep this issue open to clean up this code block, when I do.