gitweb: Fix issue with service startup when gitweb is not enabled

When gitweb is installed and not enabled without any public repos, the post_inst() method tries to enable gitweb-freedombox-auth.conf apache2 configuration. Due to new approach of symlinking configuration files only when needed, the file is not found and startup of freedombox service fails.

Fix it by making sure that gitweb auth configuration is only enabled when app itself is enabled.

Signed-off-by: Sunil Mohan Adapa sunil@medhas.org