repoview: style change in newtype() cache handling

This way of writing it does not change the logic at all,
but is more fit for the change we want to make in the
next changeset.

If anything, that's one dict lookup less in the hot path,
but that should be non measurable.

mercurial/repoview.py

@@ -472,10 +472,12 b' class repoview(object):'
 
 def newtype(base):
     """Create a new type with the repoview mixin and the given base class"""
-    if base not in _filteredrepotypes:
+    cls = _filteredrepotypes.get(base)
+    if cls is not None:
+        return cls
 
         class filteredrepo(repoview, base):
             pass
 
         _filteredrepotypes[base] = filteredrepo
-    return _filteredrepotypes[base]
+    return filteredrepo