Call forwarding's USSD parser can't skip null string.

Call forwarding's USSD parser can't handle 120*1**20*1*0#.
Parser can't handle null string.

BUG: 119806564
Test: Manual test, fake the response msg,and check call forwarding info.
Change-Id: I14757b6f2fe13bcc243a135460825aa282f8aaf1
diff --git a/src/com/android/phone/CarrierXmlParser.java b/src/com/android/phone/CarrierXmlParser.java
index 2497348..4cf7e35 100644
--- a/src/com/android/phone/CarrierXmlParser.java
+++ b/src/com/android/phone/CarrierXmlParser.java
@@ -151,6 +151,8 @@
                 for (int i = 0; i <= groupSize; i++) {
                     if (!TextUtils.isEmpty(m.group(i))) {
                         mParserStr.add(m.group(i));
+                    } else {
+                        mParserStr.add("");
                     }
                 }
             }