Hygiene: Don't create li tag if message is blank (disabled)

In the event that a wiki admin sets one of the footer link messages
to '-' (to disable it), the message gets passed as an empty string.
In that case, we should not create the li tag. Otherwise, it will
display a pipe separator with nothing to separate.

Related to...
Bug: 63414

Change-Id: I302fb84cd02bfb435b5d65d3db5e091a57fffffd
Merge "Hygiene: Don't create li tag if message is blank (disabled)"