The location which only contained "Network Watcher" resource doesn't show in the Focus Resources view after focusing it

[v-xinda]

OS: All
Build Version: v0.8.7-alpha.0
Regression: Not a regression

Repro Steps:

1. Make sure resources group by Location.
2. Focus a location only contained Network Watcher, such as "ukwest".
   
3. Check whether the focused location shows in the Focus Resources view.

Expect:
The focused location shows in the Focus Resources view.

Actual:
The focused location doesn't show in the Focus Resources view.

More Info:
If resources group by Resource Group, this issue doesn't reproduce after focusing the resource group which only contained Network Watcher.