Fix MobileNetworkSettings kotlin.UninitializedPropertyAccessException

Bug: 332477183
Test: atest MmsMessagePreferenceControllerTest

Change-Id: I849ca0f333f5246d73192ae4180b3f3ce3946d61
diff --git a/src/com/android/settings/network/telephony/MmsMessagePreferenceController.kt b/src/com/android/settings/network/telephony/MmsMessagePreferenceController.kt
index bf95475..e14d5f8 100644
--- a/src/com/android/settings/network/telephony/MmsMessagePreferenceController.kt
+++ b/src/com/android/settings/network/telephony/MmsMessagePreferenceController.kt
@@ -49,6 +49,7 @@
 
     override fun getAvailabilityStatus(subId: Int) =
         if (subId != SubscriptionManager.INVALID_SUBSCRIPTION_ID &&
+            this::telephonyManager.isInitialized &&
             !telephonyManager.isDataEnabled &&
             telephonyManager.isApnMetered(ApnSetting.TYPE_MMS) &&
             !isFallbackDataEnabled()