some messages don't have a message ID, fix it during ingest

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Traceback (most recent call last):
  File "/appenv/site-packages/twisted/internet/defer.py", line 651, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/appenv/site-packages/twisted/internet/defer.py", line 1355, in gotResult
    _inlineCallbacks(r, g, deferred)
  File "/appenv/site-packages/twisted/internet/defer.py", line 1297, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/appenv/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
--- <exception caught here> ---
  File "/appenv/site-packages/klein/storage/_sql.py", line 136, in sql
    result = yield callable(txn)
  File "/appenv/site-packages/twisted/internet/defer.py", line 1299, in _inlineCallbacks
    result = g.send(result)
  File "/appenv/site-packages/txlists/app.py", line 153, in do
    id=message['message-id'].decode('charmap'),
exceptions.AttributeError: 'NoneType' object has no attribute 'decode'