Display "No entry to save, because no text was received" after empty entry on cmdline

[apainintheneck]

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.

This PR fixes the bug mentioned in #1419. Now when the user enters an empty journal entry they get the message [Entry not saved] back whether they entered it at the command line or using an editor.

Closes #1419.

[wren]

This looks great! I just made a quick update to the error message (you did it correctly, we just changed our mind on the wording).

Thank you!