Fix NPE when activity is null

Bug:17360566
Change-Id: I20f3b0843bc8766ea1ded91b30c2662ea08cf7df
diff --git a/src/com/android/dialer/dialpad/DialpadFragment.java b/src/com/android/dialer/dialpad/DialpadFragment.java
index 141a451..9096791 100644
--- a/src/com/android/dialer/dialpad/DialpadFragment.java
+++ b/src/com/android/dialer/dialpad/DialpadFragment.java
@@ -1204,6 +1204,9 @@
      *                of the regular Dialer UI
      */
     private void showDialpadChooser(boolean enabled) {
+        if (getActivity() == null) {
+            return;
+        }
         // Check if onCreateView() is already called by checking one of View objects.
         if (!isLayoutReady()) {
             return;