TROVE-2016-10-001: out-of-bounds read on buffer chunks

Placeholder ticket; see legacy/trac#20383 (moved) for "TROVE" backronym. Fix should go out in 0.2.9.4-alpha in the next 48 hours. Severity is "Medium".

This is fixed in 0.2.8.9 and 0.2.9.4-alpha. The changelog says:

  Tor 0.2.9.4-alpha fixes a security hole in previous versions of Tor
  that would allow a remote attacker to crash a Tor client, hidden
  service, relay, or authority. All Tor users should upgrade to this
  version, or to 0.2.8.9. Patches will be released for older versions
  of Tor.

  o Major features (security fixes):
    - Prevent a class of security bugs caused by treating the contents
      of a buffer chunk as if they were a NUL-terminated string. At
      least one such bug seems to be present in all currently used
      versions of Tor, and would allow an attacker to remotely crash
      most Tor instances, especially those compiled with extra compiler
      hardening. With this defense in place, such bugs can't crash Tor,
      though we should still fix them as they occur. Closes ticket
      20384 (TROVE-2016-10-001).