Fix NPE in SyncMessage

Integer parsing in SyncMessage is throwing NPE if a field is missing.
Some fields are mandatory in a SYNC SMS, but carriers sometimes does
not send them all.

This CL refactors SyncMessage and StatusMessage so missing fields are
accounted for and all fields will have non null default value.

+ @NeededForTesting to prevent proguard from removing unused methods

Change-Id: I8af34de18cbed4484d592292aaec03456ed05af5
Fixes:29218479
6 files changed