Steps to reproduce:
1. Create a zipped mediapackages with no media in it. This can happen if a capture agent has no signals attached and throws away recording inputs.
2. Use the addZippedMediapackage to ingest that recording.
The ingest service answers with a "Bad Request" response. While this is not wrong, it leads to problems where the agent might keep trying to reingest the recording.
The ingest service should accept the media package and (potentially) deal with the missing media during workflow processing. This is to support hold operations that could put those mediapackages on hold to wait for the user to upload the media.
Merged into 1.4.x with rev 15808.