If editor contains nested editable components and the native selection enters (#692)

one of these, focus moves from the `Content` DOM element to the new active
element but editor doesn't really lose focus and selection must not be blurred.

src/components/content.js

@@ -272,6 +272,7 @@ class Content extends React.Component {
     if (this.props.readOnly) return
     if (this.tmp.isCopying) return
     if (!this.isInContentEditable(event)) return
+    if (this.element.contains(event.relatedTarget)) return
 
     const data = {}