Fix abscence of editor when editing a notification which has never been...

Fix abscence of editor when editing a notification which has never been commented. It fixes icat/E-DataPortal#157.

src/components/Event/EventContentPanel.js

@@ -32,7 +32,7 @@ class EventContentPanel extends React.Component {
 
                 if (event.type === NOTIFICATION) {
                     return (<EventContentDisplayer
-                        content={getPreviousVersionNumber(event) === 0 ? { format: 'html', text: '<p> </p>' } : event.content}
+                        content={getPreviousVersionNumber(event) === 0 ? [{ format: 'html', text: '<p> </p>' }] : event.content}
                         eventId={event._id}
                         investigationId={investigationId}
                         isEditionMode={true}