Some tweaks to HTTP live / nuplayer behaviour

- play audio-only streams again
- workaround for malformed streams that switch PIDs across bandwidths
- attempt to pick a different bandwidth stream if the previously chosen one appears
  to be malformed/unsupported.

Change-Id: I426d0a40dc725aa242f619d4c9d048b69aca55c9
related-to-bug: 2368598