contrib/wix/defines.wxi

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

<Include>

  <?if $(var.Platform) = "x64" ?>
    <?define IsX64 = yes ?>
  <?else?>
    <?define IsX64 = no ?>
  <?endif?>

</Include>