Fix server uri storage to support having no workspace

[rchiodo]

For #4037

The JupyterServerUriStorage class would throw an exception while trying to save the 'serverType' setting if the user doesn't have a workspace open. This makes the enter key actually not close the quick pick dialog.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR).
• Title summarizes what is changing.
• Has a news entry file (remember to thank yourself!).
• Appropriate comments and documentation strings in the code.
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated.
• Test plan is updated as appropriate.
• package-lock.json has been regenerated by running npm install (if dependencies have changed).

[codecov-io]

Codecov Report

Merging #4291 (dc7c53d) into main (365fab1) will increase coverage by 3%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##            main   #4291     +/-   ##
=======================================
+ Coverage     70%     74%     +3%     
=======================================
  Files        384     389      +5     
  Lines      25206   25392    +186     
  Branches    3604    3632     +28     
=======================================
+ Hits       17880   18949   +1069     
+ Misses      5929    4956    -973     
- Partials    1397    1487     +90     

Impacted Files	Coverage Δ
src/client/datascience/jupyter/serverUriStorage.ts	81% <100%> (+1%)	⬆️
...t/common/application/webviewPanels/webviewPanel.ts	10% <0%> (-58%)	⬇️
src/client/common/application/webviews/webview.ts	13% <0%> (-53%)	⬇️
.../application/webviewPanels/webviewPanelProvider.ts	43% <0%> (-50%)	⬇️
...nt/datascience/interactive-common/debugListener.ts	34% <0%> (-40%)	⬇️
...datascience/interactive-common/showPlotListener.ts	33% <0%> (-39%)	⬇️
...c/client/common/application/customEditorService.ts	25% <0%> (-33%)	⬇️
...c/client/common/application/invalidCustomEditor.ts	8% <0%> (-23%)	⬇️
src/client/datascience/dataScienceSurveyBanner.ts	69% <0%> (-20%)	⬇️
...ent/datascience/interactive-common/linkProvider.ts	16% <0%> (-19%)	⬇️
... and 96 more