Prevent possible crash by adding null pointer check

Flag: EXEMPT bug fix
Bug: 383144219
Test: manually test if it works finely
Test: atest NetworkSelectRepositoryTest NetworkSelectSettingsTest
Change-Id: I55c50c7ed9856461e00239df2a683693510fd0b7

src/com/android/settings/network/telephony/NetworkSelectRepository.kt

@@ -98,6 +98,11 @@ class NetworkSelectRepository(context: Context, private val subId: Int) {
             return emptyList()
         }
 
+        if (carrierConfigManager == null) {
+            Log.d(TAG, "carrierConfigManager is null")
+            return emptyList()
+        }
+
         val config = carrierConfigManager.getConfigForSubId(
             subId,
             CarrierConfigManager.KEY_REMOVE_SATELLITE_PLMN_IN_MANUAL_NETWORK_SCAN_BOOL