manifestcache: skip setup earlier if we don't have the lock

There a no point preparing a closure if we are not going to use it.

mercurial/manifest.py

@@ -1437,6 +1437,9 b' class manifestrevlog(object):'
             return
 
         self._fulltextcache._opener = repo.cachevfs
+        if repo._currentlock(repo._lockref) is None:
+            return
+
         reporef = weakref.ref(repo)
         manifestrevlogref = weakref.ref(self)
 
@@ -1450,7 +1453,6 b' class manifestrevlog(object):'
                 return
             self._fulltextcache.write()
 
-        if repo._currentlock(repo._lockref) is not None:
             repo._afterlock(persistmanifestcache)
 
     @property