Always show the summary if it is summoned

This ensures that the summary appears when we are showing a new
notification and switch to the overview at the same time.

Another effect of this patch is that the summary is shown if the
user moves the mouse to the bottom right corner while a notification
is being shown, which is ok.

js/ui/messageTray.js

@@ -883,7 +883,7 @@ MessageTray.prototype = {
         if (this._summaryState == State.HIDDEN) {
             if (notificationsDone && this._summaryNeedsToBeShown)
                 this._showSummary(true);
-            else if (!notificationsVisible && summarySummoned)
+            else if (summarySummoned)
                 this._showSummary(false);
         } else if (this._summaryState == State.SHOWN) {
             if (!summaryPinned)