Avoid NPE, profileFileSupplier can be null for tests

Motivation and Context

We have seen random failures for UseGlobalEndpointResolverTest and there's a red herring log when attempting to get from profileFileSupplier which can be null. This change does not fix the bug but removes the misleading warning log by avoiding dereferencing a null object.

Modifications

Testing

Screenshots (if appropriate)

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)

Checklist

[ ] I have read the CONTRIBUTING document
[ ] Local run of mvn install succeeds
[ ] My code follows the code style of this project
[ ] My change requires a change to the Javadoc documentation
[ ] I have updated the Javadoc documentation accordingly
[ ] I have added tests to cover my changes
[ ] All new and existing tests passed
[ ] I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
[ ] My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

[ ] I confirm that this pull request can be released under the Apache 2 license

aws / aws-sdk-java-v2

Avoid NPE, profileFileSupplier can be null for tests #5314