KernelSamplingMap.CorrectBorder sliced the offset span by
radius * kernelSize, so bounds narrower than the kernel radius threw
ArgumentOutOfRangeException (GaussianBlur of a 130x8 region with
sigma 10, for example), and bounds exactly equal to the radius let
Bounce offsets escape the sampling range by folding an overshoot of a
full extent to min - 1.
Route bounds no larger than the radius through an exact per-mode
correction that folds each offset into range: clamp for Repeat,
periodic reflection for Mirror and Bounce, and true modulo for Wrap.
The single-pass corrections are unchanged for larger bounds.
James Jackson-South