gitweb: don't use pathinfo for global actions

gitweb: don't use pathinfo for global actions

With PATH_INFO urls, actions for the projects list (e.g. opml,
project_index) were being put in the URL right after the base. The
resulting URL is not properly parsed by gitweb itself, since it expects
a project name as first component of the URL.

Accepting global actions in use_pathinfo is not a very robust solution
due to possible present and future conflicts between project names and
global actions, therefore we just refuse to create PATH_INFO URLs when
the project is not defined.

Signed-off-by: Giuseppe Bilotta <redacted>
Acked-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>