Fix to ensure check is done for Error.Code.NoError if Error is not null

[pieperu]

Fix for #1763

Upon discussion with @iancooper this fix won't come with any code tests as it's quite difficult to test. The only consequence of this bug, is an unnecessary call to create a topic, and the handling of a CreateTopicException - which is to just log a message.

## The output before the fix

The output after the fix

You can see from the output that after the fix, there are no longer the following message in the output:
Topic xxx is in error with code : NoError and reason : Success
and
Topic xxx already exists

[CLAassistant]

All committers have signed the CLA.

[iancooper]

@pieperu Shout if you want any advice

[iancooper]

As agreed, our transport and backing store tests are mainly automated regression tests, and TDD mostly happens in the core. Satisfied that this is the right thing to do here

[iancooper]

Thanks for this @pieperu