activation: plugin doesn't report failure to parse "go env" output

[noxer]

What version of Go, VS Code & VS Code Go extension are you using?

• Run go version to get version of Go
  • go version go1.15 windows/amd64
• Run code -v or code-insiders -v to get version of VS Code or VS Code Insiders
  • 1.48.0
  • db40434f562994116e5b21c24015a2e40b2504e6
  • x64
• Check your installed extensions to get the version of the VS Code Go extension
  • v0.16.1

Describe the bug

I managed to set the wrong GOTMPDIR using go env -w. This resulted in every call to go returning the error message go: creating work dir: CreateFile x: The system cannot find the file specified. (where x is the path I set). Now the VS Code Go plugin can't parse the return of go env anymore and doesn't work. Instead of displaying a parsing error, it either silently fails (e.g. when trying to update the Go Tools) or it displays: "Error: TypeError: Cannot read property 'lt' of undefined" (e.g. when trying to save a .go file).

Steps to reproduce the behavior:

1. Run go env -w GOTMPDIR=x
2. Open a Go project in VS Code
3. Try to save a .go file, try to update the Go tools.

[gopherbot]

Change https://golang.org/cl/253601 mentions this issue: src/goInstallTools: report go env failure