Issue Type: Bug

If you try to open the release notes while offline, then if a release notes url is configured then vscode will open it in a browser, otherwise it will do nothing, not even show an error.
Later, if you go online and try opening the release notes again, the same will happen - vscode will never attempt to open the release notes webview again.
This state is preserved until you reload the window.

Steps to Reproduce:

1. Go offline (you can also open devtools in vscode and go to the network tab and change the "online" at the top to "offline")

2. Try to open the release notes using Show Release Notes from the command palette.

3. Depending on whether you are on an official vscode build or a local build, the release notes page will be opened in your default browser. On a local build nothing happens.

4. Go back online

5. Try to open the release notes again

6. The same thing will happen

7. Reload the window using Reload Window from the command palette

8. Try to open the release notes again

9. The release notes open in a webview inside vscode

VS Code version: Code - Insiders 1.47.0-insider (6c235c7, 2020-06-26T06:20:06.931Z)
OS version: Windows_NT x64 10.0.18363
Does this issue occur when all extensions are disabled?: Yes