Submissions can be ignored on the shadow feed if source zip has 0 length file.

[johnbrvc]

Describe the issue:
In the event feeder client shadow mode, if the zip file containing the user source code (and auxiliary files) contains a zero length file, the submission is ignored and an error is generated.

To Reproduce:

1. You'll have to create a contest to shadow and act as a primary CCS.
2. Shadow the contest in another instance of PC2.
3. On the shadow, start shadowing.
4. Generate a contestant submission on the primary CCS that has a main source file and an empty auxiliary file.
5. The submission will be ignored and an error will appear on the shadow indicating the submission failed.

Expected behavior:
The submission should not be ignored and no error should occur if a source zip contains a zero length file.

Actual behavior:
As described above, the submission is tossed and an error generated.

Environment:
All.

Log Info:

Screenshots:

Additional context:
The issue is related to the fact that PC2 reads the zip as a stream. If there is a zero length file in the zip, this fails. The exact issue is described here: OpenJDK Bug Report
The solution is to save the stream to a file first, the use ZipFile to extract it.
There is a fix for this in this branch: JohnB's branch for combined scoreboards and this commit. It will be integrated in the main develop branch after regionals. Affected file: ecs/pc2/shadow/RemoteContestAPIAdapter.java