cswinrt.exe should fail (non-zero exit code) if no filtered input metadata exists

[Scottj1s]

If cswinrt.exe is misconfigured with input metadata and filtering rules, such that no input-dependent projection sources are generated, it should return a non-zero exit code.

See #892

[asklar]

Somewhat related - if the generator crashes, it does not show up as an error (it looks like a warning is issued) and it doesn't fail the build. The build will fail later when the binary it expects isn't there, but if this isn't a clean build, the build will use the prior built binary :/ ask me how I realized that :D