Ensure empty tag names are ignored / thrown out

[DanielOaks]

If we don't already, we should have tests to ensure that a tags line like this: @=53;+=ghfd doesn't result in empty tag names / a tag name that's just the c2c tag prefix. If we don't already, and if tag names must follow a specific structure / set of characters, we can add a test ensuring that too perhaps (either failing or just throwing that tag away, not sure which'd be more appropriate).