Crash occurs in SDLLifecycleManager#didEnterStateRegistered

[t-yoshii]

Bug Report

Crash occurs in SDLLifecycleManager#didEnterStateRegistered when the self.registerResponse.language = ‘-1’.

isEaualToEnum call for ‘-1’ (NSInteger) cause a crash.
https://github.com/smartdevicelink/sdl_ios/blob/master/SmartDeviceLink/SDLLifecycleManager.m#L316

registerResponse.language must be NSString, however, SDL Core can send ‘-1’ (INVALID_ENUM) when HMI returns invalid language for VR and TTS.
Related issue:
smartdevicelink/sdl_core#2230

Reproduction Steps

1. Connect SDL Proxy with HU which has invalid language value.

Expected Behavior

Crash does not occur

Observed Behavior

Crash occurs

OS & Version Information

• iOS Version: all
• SDL iOS Version: v6.1.1
• Testing Against: Our internal devboard

Test Case, Sample Code, and / or Example App

I will create PR