Matrix connector tries to parse empty messages

[colonelkrud]

Talked about this in opsdroid-general: the matrix connector tries to parse empty messages (like ones sent from the bot itself). We should avoid this by checking that the message is not None before parsing. Cadair pointed out that we can do this with if message: above L143 in the connector.

opsdroid/opsdroid/connector/matrix/connector.py

Line 143 in 11508b5

await self.opsdroid.parse(message)