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
test-convert-git.t
test-subrepo-git.t
test-patchbomb-tls.t