Koenig - Only deselect cards on cursor changes within the doc

refs TryGhost/Ghost#9505
- prevents clicks outside of the document canvas from exiting edit mode
- useful for cards that include modals because previously any click on a modal would exit edit mode and usually remove the modal from view

lib/koenig-editor/addon/components/koenig-editor.js

@@ -520,7 +520,7 @@ export default Component.extend({
         }
 
         // deselect any selected card because the cursor is no longer on a card
-        if (this._selectedCard) {
+        if (this._selectedCard && !editor.range.isBlank) {
             this.deselectCard(this._selectedCard);
         }