Fix empty note not being tall enough for menu button

www/css/notecards.css

@@ -25,6 +25,10 @@ file, You can obtain one at http://mozilla.org/MPL/2.0/.
     z-index: 99999;
 }
 
+.notecard {
+    min-height: 4em;
+}
+
 .popover .list .list-button {
     color: inherit;
 }