Simplify SmsMessage null check in writeInboxMessage.

After below change, we get a null SmsMessage instead of a null SmsMessage.mWrappedSmsMessage if there is a parsing error.

    //Do not create SmsMessage obj if it cannot be parsed correctly.
    https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/opt/telephony/+/1107247

Bug: 115692275
Test: make
Change-Id: I006cc7d9d17ad2358d07df551079db3fc4041244