IMS-VT:Process crash during MT_VT call accept scenario

-Check call is null or not to avoid NullPointerException

Change-Id: I146e6c358bd44b8a4a5fc872c1ef4f0ffe2cc5ae
CRs-Fixed: 1087615
diff --git a/InCallUI/src/com/android/incallui/InCallPresenter.java b/InCallUI/src/com/android/incallui/InCallPresenter.java
index c92151b..04d2f75 100644
--- a/InCallUI/src/com/android/incallui/InCallPresenter.java
+++ b/InCallUI/src/com/android/incallui/InCallPresenter.java
@@ -942,7 +942,9 @@
         }
 
         Call call = mCallList.getIncomingCall();
-        answerIncomingCall(context, call.getVideoState());
+        if (call != null) {
+            answerIncomingCall(context, call.getVideoState());
+        }
     }
 
     /**