Avoids java.lang.NullPointerException in WebRtcAudioRecord

webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java

Index: webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java
diff --git a/webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java b/webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java
index a13a7d552b5fcb82b5346bdbd417bdd19fb2d81d..181910a5343cf1b434a3e8a9284056902247b1d3 100644
--- a/webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java
+++ b/webrtc/modules/audio_device/android/java/src/org/webrtc/voiceengine/WebRtcAudioRecord.java
@@ -105,7 +105,9 @@ public class  WebRtcAudioRecord {
       }
 
       try {
-        audioRecord.stop();
+        if (audioRecord != null) {
+          audioRecord.stop();
+        }
       } catch (IllegalStateException e) {
         Logging.e(TAG, "AudioRecord.stop failed: " + e.getMessage());
       }