Re-selecting line tool removes current line that is being drawn

[simonpoole]

Not clear if this is intended behaviour, I would suggest doing nothing or completing the current line drawing and re-entering line drawing mode.

See https://help.openstreetmap.org/questions/56174/can-not-add-line-with-id-editor

[bhousel]

Yes, I agree we shouldn't remove the user's line.. That's a recent regression caused by these lines of code. The code is actually useful because it lets us support undo while the user draws (#3530) at the expense of throwing away all the user's work whenever something unexpected happens.

I think I can find a way to handle leaving and reentering the same mode cleanly.