Update displayTheme prference only if changed

app/src/main/kotlin/com/tutpro/baresip/ConfigActivity.kt

@@ -33,6 +33,7 @@ class ConfigActivity : AppCompatActivity() {
     private var oldCAFile = false
     private var oldLogLevel = ""
     private var callVolume = BaresipService.callVolume
+    private var oldDisplayTheme = -1
     private var save = false
     private var restart = false
     private var menu: Menu? = null
@@ -43,6 +44,7 @@ class ConfigActivity : AppCompatActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
 
         super.onCreate(savedInstanceState)
+
         binding = ActivityConfigBinding.inflate(layoutInflater)
         setContentView(binding.root)
 
@@ -100,7 +102,7 @@ class ConfigActivity : AppCompatActivity() {
         }
 
         darkTheme = binding.DarkTheme
-        val oldDisplayTheme = Preferences(applicationContext).displayTheme
+        oldDisplayTheme = Preferences(applicationContext).displayTheme
         darkTheme.isChecked = oldDisplayTheme == AppCompatDelegate.MODE_NIGHT_YES
 
         debug = binding.Debug
@@ -246,6 +248,7 @@ class ConfigActivity : AppCompatActivity() {
                     AppCompatDelegate.MODE_NIGHT_YES
                 else
                     AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM
+                if (oldDisplayTheme != newDisplayTheme)
                     Preferences(applicationContext).displayTheme = newDisplayTheme
 
                 var logLevelString = "2"