Don't redo into un-annotated edit states

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The way history.redo() is implemented, it's possible to redo into an un-annotated edit state. This is really bad because the user could perform some temporary edit, then undo out of it, and then redo back into the temporary edit state.

For example, here is me starting to draw an area, then undoing the area, and then redoing back into the state with the temporary area (it's a degenerate area with only 2 nodes).

It's also amusing because the "Redo" button says "Nothing to redo" and appears disabled, but you can still click on it to redo into the temp state anyway.