GUACAMOLE-896: Ensure "seeking" class not erroneously assigned if seek() finishes immediately.

doc/guacamole-playback-example/src/main/webapp/playback.js

@@ -211,6 +211,9 @@
     // Seek within recording if slider is moved
     positionSlider.onchange = function sliderPositionChanged() {
 
+        // Seek is in progress
+        player.className = 'seeking';
+
         // Request seek
         recording.seek(positionSlider.value, function seekComplete() {
 
@@ -219,9 +222,6 @@
 
         });
 
-        // Seek is in progress
-        player.className = 'seeking';
-
     };
 
 })();