Check for error codes in $zf(-100) calls

e.g., this should be treated as an error:

```
Building in 1 stage(s).
Running in background: npm run --prefix C:\Users\... build --node-flags --max-old-space-size=8000 -- --baseHref=...--progress=false
'npm' is not recognized as an internal or external command,
operable program or batch file.
Angular build process completed.
```