Don't write history in the middle of draw_line/draw_way, etc

[bhousel]

It turns out that it is really easy to create a lot of these degenerate geometries in iD that we've spent years trying to track down. (1-node ways, 2-node areas, etc)

1. Start drawing a thing
2. ⌘R Refresh your browser
3. Restore history
4. Partially drawn thing exists.. Oops! 😱

So we should really disable history writes while the user is in the process of drawing stuff.

[tyrasd]

Excellent find, Bryan! I almost can't believe it was something that "obvious".