Buffer writer fix

[tonystone]

Description

Fixing a crash when buffering is on and the buffer is empty when it attempts to write.

Motivation and Context

How Has This Been Tested?

This fix is currently being tested in a pre-release application during the QA cycle.

Checklist:

For all changes:

• Is there an issue associated with this PR? Is it referenced
  in the commit message?
• Has your PR been rebased against the latest commit within the target branch (typically master)?
• Is your initial contribution a single, squashed commit?

For code changes:

• Avoid other runtime dependencies
• Have you written or updated unit tests to verify your changes?
• Have you ensured that the full suite of tests is executed via make tests in the cmake-build-debug` directory off the root of the project?
• If applicable, have you updated the documentation?
• If applicable, have you updated the CHANGELOG.md file?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check travis-ci for build issues and submit an update to your PR as soon as possible.