The "Syncing changes..." message is wrongly loops continuously after an empty note is deleted

[Softvision-MariusComan]

[Affected versions]:

• Firefox 60.0 and above

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with the latest version of the "Firefox Notes" add-on (4.1.0dev custom built on 11.05.2018) installed.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Click the "New Note" button from the top part of the sidebar.
3. Click the menu button from the right part of the title bar.
4. Select the "Delete Note" option and observe the bottom part of the sidebar.

[Expected result]:

• The "Synced at [Hour] message is displayed.

[Actual result]:

• The "Syncing changes..." message is displayed in a continuous loop.

[Notes]:

• The issue is reproducible if you delete all the content from a note before deleting the note itself.
• This issue is also reproducible with the TxP version of "Firefox Notes".
• The issue is no longer reproducible after the sidebar is reopened.
• Attached a screen recording of the issue: