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.
I don't really feel that we need tests like this, but still added for the new error code as similar tests exist for the rest of error codes.