zeroconf: access repo on hgweb_mod properly (issue5036)

hgweb_mod.hgweb.repo disappeared in ae33fff17c1e (hg: establish
a cache for localrepository instances) and the code for accessing repo
instances from hgweb was later refactored to go through a cache-aware
context manager.

Adapt zeroconf to access the repo instance via the new API.

hgext/zeroconf/__init__.py

@@ -113,9 +113,10 b' def zc_create_server(create_server, ui, '
         repos = app.repos
     except AttributeError:
         # single repo
-        name = app.reponame or os.path.basename(app.repo.root)
-        path = app.repo.ui.config("web", "prefix", "").strip('/')
-        desc = app.repo.ui.config("web", "description", name)
+        with app._obtainrepo() as repo:
+            name = app.reponame or os.path.basename(repo.root)
+            path = repo.ui.config("web", "prefix", "").strip('/')
+            desc = repo.ui.config("web", "description", name)
         publish(name, desc, path, port)
     else:
         # webdir