bundle2: seek in part iterator

When iterating over bundle2 parts, add a seek to the iterator so that
processing will continue normally even if the entire part isn't
consumed.

mercurial/bundle2.py

@@ -590,6 +590,7 b' class unbundle20(unpackermixin):'
         while headerblock is not None:
             part = unbundlepart(self.ui, headerblock, self._fp)
             yield part
+            part.seek(0, 2)
             headerblock = self._readpartheader()
         self.ui.debug('end of bundle2 stream\n')