changegroup: invert conditional and dedent

I don't like seeing code that visually resembles the pyramid of
doom.

Differential Revision: https://phab.mercurial-scm.org/D4197

mercurial/changegroup.py

@@ -1048,7 +1048,10 b' class cgpacker(object):'
             dir, nodes = tmfnodes.popitem()
             store = dirlog(dir)
             prunednodes = self._prune(store, nodes, commonrevs)
-            if not dir or prunednodes:
+
+            if dir and not prunednodes:
+                continue
+
                 lookupfn = makelookupmflinknode(dir, nodes)
 
                 if self._ellipses:
@@ -1062,6 +1065,7 b' class cgpacker(object):'
                                              clrevtolocalrev):
                     size += len(x)
                     yield x
+
         self._verbosenote(_('%8.i (manifests)\n') % size)
         yield self._manifestsend