hgweb: simplify the handling of empty repo
This abstraction have two advantages:
- If the revlog is empty, None of the code bellow is relevant,
early returns seems a win.
- Abtraction of the 'emptiness' check will help later when we stop relying on
nodefunc.
A bonus, with filtering, a non-empty revlog may not have '0' revision
accessible. It'll be easier to handle with the emptiness test in a dedicated
function
@echo off
rem launch hg.exe from parent folder
"%~dp0\..\hg.exe" %*