Cancel when drawing tulip road in walkthrough causes freeze

[shbgr]

If you cancel the drawing operation of tulip road (in walkthrough) the browser freezes completely (at least in Chrome).
Seems like drawWay.cancel() gets stuck in an infinite loop here:

while (context.graph() !== startGraph) {
   context.pop();
}

How to reproduce

• start walkthrough
• select "lines"
• start drawing tulip road
• cancel with ESC or by clicking the first node again
• browser freezes

[bhousel]

Thanks for reporting @shbgr