Added TryComplete instead of comple during channel shutdown

[patriktiain]

Proposed Changes

Change from Threading.Channel.Complete() to TryComplete() to catch any race conditions. Race condition can occur if another thread already have called complete on this channel.

Types of Changes

What types of changes does your code introduce to this project?
Put an x in the boxes that apply

• Bug fix for The Channel has been closed exception from HeartBeatReadCallback #1884
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments