Fix request thread is blocked due to call API answerRingCall

Wake up the requesting thread after answering the ring call

Change-Id: Ia46cbc8ad793068476f2fe867a46b23a4ef0313f
diff --git a/src/com/android/phone/PhoneInterfaceManager.java b/src/com/android/phone/PhoneInterfaceManager.java
index 2c4ebee..78e22ae 100644
--- a/src/com/android/phone/PhoneInterfaceManager.java
+++ b/src/com/android/phone/PhoneInterfaceManager.java
@@ -362,6 +362,11 @@
                     request = (MainThreadRequest) msg.obj;
                     int answer_subId = request.subId;
                     answerRingingCallInternal(answer_subId);
+                    request.result = ""; // dummy result for notifying the waiting thread
+                    // Wake up the requesting thread
+                    synchronized (request) {
+                        request.notifyAll();
+                    }
                     break;
 
                 case CMD_END_CALL: