Impure Cast Nodes Can be Converted to Pure While the Blueprint Graph is Read-Only

Cast nodes can be converted to pure while the blueprint graph is in read-only mode, such as when you are debugging the blueprint.

Found in 4.14.0 CL# 3195953. Reproduced in 4.13.2 CL# 3172292 and 4.15 Main CL# 3205566

1. Open the editor (First Person Project)
2. Add an OnComponentBegin overlap event for one of the component's in the FirstPersonCharacter
3. Drag off OtherActor and cast to one of the actors in the list
4. Add a breakpoint on the Branch node after BeginPlay
5. Press the Play Button
6. While the graph is paused after the breakpoint is hit, right-click on the cast node and select Convert to Pure.

Result: Notice that the cast node is converted to a pure cast node.

Expected: The node would not be able to be converted while the graph is in read-only mode.