Blender Git Loki

Fix T86967 : Artifacts when tracing image to Grease Pencil

Tracing images to grease pencil objects creates sometimes artifacts, as seen, for example, when tracing the attached image. {F9910821}
I have found the same behavior both in the 2.92 release and in the current 2.93 master.
The artifacts are caused by a variable that's not initialized or updated when finding a point tagged as POTRACE_CORNER.
This patch solves this issue.

Maniphest Tasks: T86967

Differential Revision: https://developer.blender.org/D10832