revset: reduce dict lookup in lazyset.__contains__

Avoid an extra dict lookup when we have to compute the value. No
visible performance impact but this shaves the yak a few extra
nanometers.

mercurial/revset.py

@@ -2342,7 +2342,8 b' class lazyset(object):'
     def __contains__(self, x):
         c = self._cache
         if x not in c:
-            c[x] = x in self._subset and self._condition(x)
+            v = c[x] = x in self._subset and self._condition(x)
+            return v
         return c[x]
 
     def __iter__(self):