BUG: Remap always switches to red channel

[andyp123]

Remap only seems to affect the red channel when used.

[andyp123]

This has been fixed by exposing the RGBA channels in the redo and storing the value of active channels on the operator when the operation is applied. However, I do not believe this issue was present in older versions of Blender, so it could be caused by a bug in Blender. This needs further investigation.

The issue is still present in both Invert and Posterize, which use the RGBA channels in a similar way. Upon changing values in the redo panel, the channel used for the operation will revert to some other channel (seemingly the last one used for another operation).