Output channel doesn't exist with `gitlens.outputLevel` default

- I tried to apply a stash, it failed. 
- A notification told me to find more details in the output channel. 
- I clicked "Open output channel", nothing happened

I had to read the source to find that the output channel isn't created when the "output level" setting is silent, which is the default value. It seems like "errors" would be a more useful default.