Fixed #9024 - API returns error when Note lacks attachment

[tsummerer]

Description

The API incorrectly assumes that if the filename attribute exists, that the client is attempting to perform an upload. This is not always the case and in fact, many clients will return many of the attributes that are provided by a GET request.

The PR makes the application check if the filename is Not Empty before assuming that a file upload is in progress.

Motivation and Context

This fixes #9024
It builds on #8408

How To Test This

1. Create a Note with no attachment
2. Attempt to Edit the note by performing a PATCH request with a blank (empty string) filename attribute.
   The request should succeed.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.