0.89: Mosaic Bug when using Spacing

[Stiven]

XnView: MP 0.89 - 64 bit
OS: Windows 64bit

Hello,

When I want to merge 5 images, and when I'm using mosaic option with spacing enabled to be 1 or more. The last spacing is doubled or trippled, and I always need to edit the images so I cut the last spacing width.

Example: https://imgur.com/y96bGo0

Effect: Image generating is bad with last spacing.

To reproduce:
1. Pick 5 images
2. Go to Creatre - JOin Images
3. check mosaic
4. check spacing
5. put 10 as value
6 see the problem in generated image

[xnview]

Thanks to your detailed description I can reproduce the problem.