httpconnection: make sure to clear progress of httpsendfile at EOF

read() should never raise EOFError. If it did, UnboundLocalError would occur
due to unassigned 'ret' variable.

This issue was originally reported to TortoiseHg:
https://bitbucket.org/tortoisehg/thg/issues/4707/

mercurial/httpconnection.py

@@ -44,10 +44,10 b' class httpsendfile(object):'
         self._total = self.length // 1024 * 2
 
     def read(self, *args, **kwargs):
-        try:
-            ret = self._data.read(*args, **kwargs)
-        except EOFError:
+        ret = self._data.read(*args, **kwargs)
+        if not ret:
             self.ui.progress(_('sending'), None)
+            return ret
         self._pos += len(ret)
         # We pass double the max for total because we currently have
         # to send the bundle twice in the case of a server that