Target with no valid files is considered as having 0% coverage

[diogomusou]

If all files in a target are invalid (ignored files), the target shows up as having 0% coverage. The total coverage is also reduced. Because of this I had to include this target in "excluded_targets".

I believe it would be best to show it as having 100% coverage, or not including it at all.

By having to include the target in "excluded_targets" it's easy to miss it in case valid files are added to the target later.