Update ALAudioRenderer: enhanced log message

jme3-core/src/main/java/com/jme3/audio/openal/ALAudioRenderer.java

@@ -1447,6 +1447,12 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
                 return;
             }
 
+            AudioData audioData = src.getAudioData();
+            if (audioData == null) {
+                logger.log(Level.WARNING, "pauseSource called on source with null AudioData: {0}", src);
+                return;
+            }
+
             if (src.getStatus() == Status.Playing) {
                 assert src.getChannel() != -1;
 
@@ -1471,6 +1477,12 @@ public class ALAudioRenderer implements AudioRenderer, Runnable {
                 return;
             }
 
+            AudioData audioData = src.getAudioData();
+            if (audioData == null) {
+                logger.log(Level.WARNING, "stopSource called on source with null AudioData: {0}", src);
+                return;
+            }
+
             if (src.getStatus() != Status.Stopped) {
                 int channel = src.getChannel();
                 assert channel != -1; // if it's not stopped, must have id