Issue Type: Bug

Testing microsoft/vscode#64262.

1. Create a PR using the extension
2. Open a file that's part of the PR (and make it stick)
3. Open the overview page of the PR
4. Merge the PR on the overview page
5. Hit the Exit Review Mode button
6. Switch to the editor from step 2)
   -> Commenting range indicators are still there.

Extension version: 0.3.1
VS Code version: Code - Insiders 1.30.0-insider (fa87e67ebfd6b8014ba697ddbc6c2d6c0e2cb970, 2018-12-04T09:26:33.257Z)
OS version: Darwin x64 18.0.0