Content is not saved to current frame when scrubbing while drawing.

[MrStevns]

Issue Summary

While drawing (Yes, literally while drawing), moving to a different frame, means that the stroke you're currently drawing, will be painted to the frame where the stroke is stopped.

Consider the following: You have two frames, frame 1 where there's already a drawing, frame two where you're currently drawing. If you use the shortcuts to switch frame, while drawing and let go on frame 1, then the content that was started on frame 2, will be painted on frame 1, causing modification to your first frame, while the second frame is still empty.

Actual Results

Moving to a different frame while drawing, causes the newest stroke to appear on the frame that was moved to.

Expected Results

Moving to a different frame while drawing, should save the the content to the frame where the stroke was started, then move and continue drawing from where it left off, if the user is still drawing.

Visual

Notes

The bug was discovered by a user.

[Kaikogf]

@CandyFace While following your steps to reproduce the issue, I found another issue, it may be related to yours. I will post it in a moment (here it is #1465)