rtrim() input before checking if note form is empty

##### What does this MR do?

This PR prevents the `Add Comment` button to get activated when only entering whitespace. This is done be doing an `rtrim` before checking if the input is empty.

##### Why was this MR needed?

Currently when entering a comment with only whitespace, the `Add comment` button gets activated.

@jvanbaarsen Can you take a look? :innocent: