FM2: Fix the issue with MO call

Fix the issue with null pointer exception.
Added a check before access.

Change-Id: Ieb32cba666dca9914e9d24722088323bdd229371
diff --git a/fmapp2/src/com/caf/fmradio/FMRadioService.java b/fmapp2/src/com/caf/fmradio/FMRadioService.java
index 25ceeb2..ec080bb 100644
--- a/fmapp2/src/com/caf/fmradio/FMRadioService.java
+++ b/fmapp2/src/com/caf/fmradio/FMRadioService.java
@@ -387,7 +387,9 @@
 
     private synchronized void exitRecordSinkThread() {
         stopRecordSink();
-        mRecordSinkThread.interrupt();
+        if (mRecordSinkThread != null) {
+            mRecordSinkThread.interrupt();
+        }
         mRecordSinkThread = null;
     }