Dragging a block off the edge breaks undo in fixed size workspaces

[RoboErikG]

Problem statement

If you drag a block out of bounds in a fixed size workspace such that it is snapped back to the edge of Blockly Undo becomes unable to go past that event.

Expected Behavior

Undo can revert changes back to the start.

Actual Behavior

The undo stack gets stuck.

Steps to Reproduce

1. go to https://blockly-demo.appspot.com/static/demos/fixed/index.html
2. Drag two blocks onto the workspace
3. Drag one of the blocks down past the edge of the browser window and release so it snaps back to the edge of the workspace.
4. Do any number of other changes.
5. Try to undo back past the snapped drag.

Stack Traces

No error reported.

Operating System and Browser

• Desktop Chrome