fix: do not throw on empty resource files

[emazv72]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

If a component references an empty resource file (styleUrls) npm run lib:build throws an error while inlining.

• What is the current behavior? (You can also link to an open issue here)

This typically happens when you generate a component with angular-cli like this:

ng generate component

The css generated for the component is empty.
angular-cli can handle empty resource files and doesn't throw.

• What is the new behavior (if this is a feature change)?

This PR tries to fix the issue.

• Other information:

[monutam91]

A huge +1 on this, because it caused the errors for me as well, but VSCode's terminal did not dropped an error for me just frozed for good.