[Migrated] Handling non-dict SNS messages

[jneves]

Originally from: Miserlou/Zappa#2198 by piotrdrazikowski

Description

The main SNS message handler incorrectly assumes that every message that was parsed using json.loads() without throwing an exception is of dict type, and then uses dict methods like .get() on the parsed object which eventually leads to a crash. In our case this has prevented us from sending a list of dicts, but there's more examples. This PR fixes it by handling the AttributeError exception

GitHub Issues

Miserlou/Zappa#1466
Miserlou/Zappa#1864