Looks like almost everywhere else, the v2d mask size is calculated
as "v2d->mask size plus one". This is the zoom ratio that the V2D
resizing tries to keep constant, etc.
However the VSE timeline drawing code, when calculating the pixel
scaling factors, used the v2d->mask size without adding +1.
This resulted in a very slight zoom ratio change when resizing the
timeline area, which is made larger because thumbnails are often more
wide than narrow, and many of them are laid out next to each other.
Pull Request: https://projects.blender.org/blender/blender/pulls/142952
71ad809bbe