Fix NPE in CallCard if we didn't actually dial a "number"

Bug: 3085116
Change-Id: I667e573f482555368ba3eb19dc52edea9eba4be0
diff --git a/src/com/android/phone/CallCard.java b/src/com/android/phone/CallCard.java
index 03f5c96..2fe588c 100755
--- a/src/com/android/phone/CallCard.java
+++ b/src/com/android/phone/CallCard.java
@@ -1079,7 +1079,7 @@
             // Then we could remove this hack, and instead ask the CallerInfo
             // for a "user visible" form of the SIP address.
             String number = info.phoneNumber;
-            if (number.startsWith("sip:")) {
+            if ((number != null) && number.startsWith("sip:")) {
                 number = number.substring(4);
             }