util: improve handling of truncated compressed streams

If the compressed stream is over as marked by the reader providing
nothing new and the compression engine is not providing data, bail out.
This can happen in practise when the server misbehaves and would result
in an infinite loop otherwise.

Differential Revision: https://phab.mercurial-scm.org/D4297

mercurial/util.py

@@ -3377,6 +3377,9 b' class _CompressedStreamReader(object):'
                 return ''.join(buf)
             chunk = self._reader(65536)
             self._decompress(chunk)
+            if not chunk and not self._pending and not self._eof:
+                # No progress and no new data, bail out
+                return ''.join(buf)
 
 class _GzipCompressedStreamReader(_CompressedStreamReader):
     def __init__(self, fh):