loganalyzer: Prevent duplicate messages

[prgmitchell]

Description

Keep a record of messages that have already been added to prevent duplicates.

Motivation and Context

Saw this log with two "Capture Interference" messages: https://obsproject.com/logs/3uhJYYDLFiwJJiBz

How Has This Been Tested?

Tested with the above log.

Currently:

This PR:

Types of changes

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

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.