Edge drawing feedback doesn't start at the correct position

[AndrewJakubowicz]

Issue description

When you are drawing the edges, the feedback doesn't always line up correctly.

Steps to reproduce the issue

1. Place the mouse in edge drawing mode.
2. Start drawing an edge.

What's the expected result?

The feedback line should line up with the initial node.

What's the actual result?

Currently the line doesn't line up and floats in the middle of the canvas.