Disable 'Save changes' button if input is empty, fixes #6351

Created by: Razer6

What does this MR do?

This PR deactivates the save button of a note, if the input is empty (similar as creating a note). Additionally, it changes the class of the Choose File button to be the size as when creating a note

Why was this MR needed?

Currently it's possible to edit a comment to be empty.

What are the relevant issue numbers / Feature requests?

This PR fixes #6351 (closed)

Screenshots

Before

After

@jvanbaarsen Can you take a look?