Fix crash in voicemail notifications.

Ending up with an NPE because of a non-existent URI.

Bug: 21004150
Change-Id: If06a05461a392fcbb2ed750dea2f8a0deb5bbd80
diff --git a/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java b/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
index 61f8635..8241811 100644
--- a/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
+++ b/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
@@ -143,7 +143,7 @@
                 }
             }
             // Check if this is the new call we need to notify about.
-            if (newCallUri != null &&
+            if (newCallUri != null && newCall.voicemailUri != null &&
                     ContentUris.parseId(newCallUri) == ContentUris.parseId(newCall.voicemailUri)) {
                 callToNotify = newCall;
             }