Fix NPE in onPostDialCharWait

Handle calls to onPostDialCharWait when mInCallActivity is null.

Bug:12021342
Change-Id: Id8da6074f7bd3a0c0962dbaa9246c2de18e6e38b
(cherry picked from commit 01563b04e60e34845ed57d8bb0e90ed01c8462ab)
diff --git a/src/com/android/incallui/InCallPresenter.java b/src/com/android/incallui/InCallPresenter.java
index 8bec492..1402621 100644
--- a/src/com/android/incallui/InCallPresenter.java
+++ b/src/com/android/incallui/InCallPresenter.java
@@ -425,7 +425,9 @@
     }
 
     public void onPostDialCharWait(int callId, String chars) {
-        mInCallActivity.showPostCharWaitDialog(callId, chars);
+        if (isActivityStarted()) {
+            mInCallActivity.showPostCharWaitDialog(callId, chars);
+        }
     }
 
     /**