Check if stream exists before unsetting preferred URI

[ostap0207]

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Pull Request Details

JIRA link(s):

#95

maybeUnsetPreferredUri function was added in this commit:
b2b6543

This caused unhandled error for some flows, such as when user
denies microphone access.

To fix this, we should check if the stream even exists before
attempting to calling updatePreferredURI on it.

Before review

• Updated CHANGELOG.md if necessary
• Added unit tests if necessary
• Updated affected documentation
• Verified locally with npm test
• Manually sanity tested running locally
• Ready for review

Before merge

• Got one or more +1s
• Squashed erroneous commits if necessary
• Re-tested if necessary

[charliesantos]

Thanks for submitting @ostap0207 . I resubmitted your PR here #144 and added my original comments and also a changelog. I'll close this now.