Check Messages before Parsing

[mugoh]

Description

The matrix connector attempts to parse empty messages. This issue is solved by checking the message has a value before calling the parsing function.

Fixes #905

Status

READY

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Tox tests pass locally

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

Merging #913 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #913   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          34     34           
  Lines        2198   2198           
=====================================
  Hits         2198   2198

Impacted Files	Coverage Δ
opsdroid/connector/matrix/connector.py	100% <ø> (ø)	⬆️

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[FabioRosado]

Thank you so much for working on this issue @hogum I am going to merge this PR now.
We send opsdroid stickers to new contributors so if you would like yours send a DM with your address to opsdroid twitter and we will send you some 😄 👍

[mugoh]

Thank you for the warm welcome @FabioRosado 😄