Mouse remains dragging state even if you release middle mouse button outside of canvas.
Hi! I found a minor bug.
steps to reproduce:
1. Holding Middle Mouse Button anywhere and move outside of canvas( e.g. side panel )
2. Release MMB and move inside of canvas.
3. Now it remains dragging state until you click MMB again. If you click LMB, canvas view would jump to somewhere uncontrolled.

Expect behaviour:
Mouse exit dragging state when release middle mouse button outside of canvas.