Fixing Broadcast processor dropping telemetry items

[RamjotSingh]

Fix Issue #994
Fixing issue where BroadcastProcessor was dropping TelemetryItems due to race condition.

• I ran Unit Tests locally.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public surface reviewed
• CHANGELOG.md updated with one line description of the fix, and a link to the original issue.
• The PR will trigger build, unit test, and functional tests automatically. If your PR was submitted from fork - mention one of committers to initiate the build for you.

[RamjotSingh]

@SergeyKanzhelev , @cijothomas Please trigger build.