Blender Git Loki

GPencil: Fix unreported missing frames in interpolation

When interpolate, the temp frames are tagged, and later removed. If for any reason any stroke was tagged in other area of Blender (this tag is used for temp tagging), the stroke could be removed by error when run interpolation.

In a previous fix, the tag was cleared before, but only for the frame range of the interpolation. Now, the clear is done for all frames.

Also, instead to clear for each stroke sampling, now it's done only once at invoke time.