Bug 990020 - [B2G][SMS] A MMS that has not been downloaded yet will display a "Missing SIM card" message after changing the SIM to a different valid one. r=julien

There are two commits here:
* Base fix;
* Refactoring of Messaging API error code.
Currently we just notify user about SIM mismatch, but should we try to download with the second SIM in case of Dual SIM, like seems we do for other error code?