fix NEP-5 query eventhub exception

What current issue(s) does this address, or what feature is it adding? Discord user Marcello#6271 reported an error where an exception is thrown upon contract deployment. Specifically

Traceback (most recent call last):
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/neo/Wallets/NEP5Token.py", line 101, in Query
    engine = ApplicationEngine.Run(snapshot, sb.ToArray(), exit_on_error=True, gas=Fixed8.FromDecimal(10.0), test_mode=False)
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/neo/SmartContract/ApplicationEngine.py", line 201, in Run
    events.emit(event.event_type, event)
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/pymitter/init.py", line 282, in emit
    remove = [l for l in listeners if not l(args, **kwargs)]
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/pymitter/init.py", line 282, in <listcomp>
    remove = [l for l in listeners if not l(args, kwargs)]
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/pymitter/init.py", line 310, in call
    self.func(*args, kwargs)
  File "/home/marcello/neoproject/venv/lib/python3.7/site-packages/neo/EventHub.py", line 62, in on_sc_event
    logger.info("[%s][%s] [%s] [tx %s] %s" % (sc_event.event_type, sc_event.block_number, sc_event.contract_hash, sc_event.tx_hash.ToString(), payload.ToJson(auto_hex=False)))
AttributeError: 'NoneType' object has no attribute 'ToString'

Upon investigation I found that when a contract is deployed, neo-python tries to determine if the contract is a NEP-5 contract. It does this by running the VM and trying to query known methods of a nep-5 contract. This query mechanism runs the VM without setting up a container (Transaction) that the query is ran from. In a normal case VM execution is always triggered from a invocation transaction so this error would not occur.

How did you solve this problem? fix initialization of the VM for NEP-5 queries by using a fake/empty TX as container

How did you make sure your solution works? manually reproduced the issue before and after the fix

Are there any special changes in the code that we should be aware of?

Please check the following, if applicable:

[ ] Did you add any tests?
[X] Did you run make lint?
[X] Did you run make test?
[X] Are you making a PR to a feature branch or development rather than master?
[X] Did you add an entry to CHANGELOG.rst? (if not, please do)

CityOfZion / neo-python

fix NEP-5 query eventhub exception #1026