Fix #5455: Resolve crash in AudioViewModel by initializing state variables

app/src/main/java/org/oppia/android/app/player/audio/AudioViewModel.kt

@@ -1,5 +1,6 @@
 package org.oppia.android.app.player.audio
 
+import android.util.Log
 import androidx.databinding.ObservableBoolean
 import androidx.databinding.ObservableField
 import androidx.lifecycle.LiveData
@@ -66,11 +67,16 @@ class AudioViewModel @Inject constructor(
     processPlayStatusLiveData()
   }
 
-  fun setStateAndExplorationId(newState: State, id: String) {
+  fun setStateAndExplorationId(newState: State?, id: String?) {
+    if (newState == null || id == null) {
+      Log.e("AudioViewModel", "Failed to set state or id - parameters are null")
+      return
+    }
     state = newState
     explorationId = id
   }
 
+
   fun loadMainContentAudio(allowAutoPlay: Boolean, reloadingContent: Boolean) {
     hasFeedback = false
     loadAudio(contentId = null, allowAutoPlay, reloadingContent)
@@ -88,6 +94,11 @@ class AudioViewModel @Inject constructor(
    * @param allowAutoPlay If false, audio is guaranteed not to be autoPlayed.
    */
   private fun loadAudio(contentId: String?, allowAutoPlay: Boolean, reloadingMainContent: Boolean) {
+    if (!::state.isInitialized || !::explorationId.isInitialized) {
+      Log.w("AudioViewModel", "Cannot load audio: state or explorationId is not initialized.")
+      return
+    }
+
     val targetContentId = contentId ?: state.content.contentId
     val voiceoverMapping =
       state.recordedVoiceoversMap[targetContentId] ?: VoiceoverMapping.getDefaultInstance()