Fix potential NPE in DefaultVoicemailNotifier

Don't try to format an empty number

Bug: 26095129
Change-Id: I6356c24e03066babd22217b24004f9ae9a53a67b
diff --git a/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java b/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
index c40c993..2b894a1 100644
--- a/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
+++ b/src/com/android/dialer/calllog/DefaultVoicemailNotifier.java
@@ -154,7 +154,7 @@
                 if (TextUtils.isEmpty(name)) {
                     // Look it up in the database.
                     name = mNameLookupQuery.query(newCall.number);
-                    if (TextUtils.isEmpty(name)) {
+                    if (TextUtils.isEmpty(name) && !TextUtils.isEmpty(newCall.number)) {
                         name = PhoneNumberUtils.formatNumber(newCall.number, newCall.countryIso);
                     }
                 }