Fix crash when mWrappedMessageData is null.

Sometimes the internal mWrappedMessageData object of SmsMessageBase is
empty, prevent a crash when parsing the SMS message by checking if it is
null.

Bug: 20858675
Change-Id: Ia83f6c2e93c2d4de5a4211fd35b60600a6638914
diff --git a/src/com/android/phone/vvm/omtp/sms/OmtpMessageReceiver.java b/src/com/android/phone/vvm/omtp/sms/OmtpMessageReceiver.java
index b9cb4ff..7e6d645 100644
--- a/src/com/android/phone/vvm/omtp/sms/OmtpMessageReceiver.java
+++ b/src/com/android/phone/vvm/omtp/sms/OmtpMessageReceiver.java
@@ -53,7 +53,9 @@
         StringBuilder messageBody = new StringBuilder();
 
         for (int i = 0; i < messages.length; i++) {
-            messageBody.append(messages[i].getMessageBody());
+            if (messages[i].mWrappedSmsMessage != null) {
+                messageBody.append(messages[i].getMessageBody());
+            }
         }
 
         WrappedMessageData messageData = OmtpSmsParser.parse(messageBody.toString());