bundlerevlog: use for loop over iterator instead of while True

The iter() builtin has a neat pattern where you give it a callable of
no arguments and a sentinel value, and you can then loop over the
function calls like a normal iterator. This cleans up the code a
little.

mercurial/bundlerepo.py

@@ -56,10 +56,8 b' class bundlerevlog(revlog.revlog):'
         self.repotiprev = n - 1
         chain = None
         self.bundlerevs = set() # used by 'bundle()' revset expression
-        while True:
-            chunkdata = bundle.deltachunk(chain)
-            if not chunkdata:
-                break
+        getchunk = lambda: bundle.deltachunk(chain)
+        for chunkdata in iter(getchunk, {}):
             node = chunkdata['node']
             p1 = chunkdata['p1']
             p2 = chunkdata['p2']