Toolbar doesn't close after hyperlinking an image

[jaclynong]

Prelude

The issue described in #848 still exists for Chrome. I was not able to reproduce it in IE/Edge/Firefox.

The issue is that the linkSelectionTest does not check if the selectionData.element has any value (similar to what imageSelectionTest is checking).

Reproduce

1. Download AlloyEditor 1.5.15 source.
2. Modify index.html to import the non-minified version of alloy-editor.
   <script src="alloy-editor/alloy-editor-all.js"></script>
3. Modify alloy-editor-all.js to add 'link' button to image toolbar.
   buttons: ['imageLeft', 'imageCenter', 'imageRight', 'link']
4. Open the editor with Chrome.
5. Add an image or click the existing one.
6. Add a hyperlink by either hitting Enter or clicking the check mark.

Result :
On submission the toolbar isn't closed. However the toolbar closes when hyperlinking text.

Acceptance Criteria

1. Hyperlinking toolbar closes after submission.
2. Test in Chrome, IE11, Edge, and FireFox.

[jaclynong]

I'll create a PR shortly.