fmod: return NullAudioSound if file does not exist

This matches the OpenAL behaviour, and is needed to fix the unit tests on macOS.

panda/src/audiotraits/fmodAudioManager.cxx

@@ -419,15 +419,19 @@ get_sound(const std::string &file_name, bool positional, int) {
   VirtualFileSystem *vfs = VirtualFileSystem::get_global_ptr();
   vfs->resolve_filename(path, get_model_path());
 
-  // Build a new AudioSound from the audio data.
-  PT(AudioSound) audioSound;
-  PT(FmodAudioSound) fmodAudioSound = new FmodAudioSound(this, path, positional);
-
-  _all_sounds.insert(fmodAudioSound);
-
-  audioSound = fmodAudioSound;
-
-  return audioSound;
+  // Locate the file on disk.
+  path.set_binary();
+  PT(VirtualFile) file = vfs->get_file(path);
+  if (file != nullptr) {
+    // Build a new AudioSound from the audio data.
+    PT(FmodAudioSound) sound = new FmodAudioSound(this, file, positional);
+
+    _all_sounds.insert(sound);
+    return sound;
+  } else {
+    audio_error("createSound(" << path << "): File not found.");
+    return get_null_sound();
+  }
 }
 
 /**

panda/src/audiotraits/fmodAudioSound.cxx

@@ -39,9 +39,10 @@ TypeHandle FmodAudioSound::_type_handle;
  */
 
 FmodAudioSound::
-FmodAudioSound(AudioManager *manager, Filename file_name, bool positional) {
+FmodAudioSound(AudioManager *manager, VirtualFile *file, bool positional) {
   ReMutexHolder holder(FmodAudioManager::_lock);
-  audio_debug("FmodAudioSound::FmodAudioSound() Creating new sound, filename: " << file_name  );
+  audio_debug("FmodAudioSound::FmodAudioSound() Creating new sound, filename: "
+              << file->get_original_filename());
 
   _active = manager->get_active();
   _paused = false;
@@ -77,20 +78,14 @@ FmodAudioSound(AudioManager *manager, Filename file_name, bool positional) {
   _manager = fmanager;
 
   _channel = 0;
-  _file_name = file_name;
+  _file_name = file->get_original_filename();
   _file_name.set_binary();
 
   // Get the Speaker Mode [Important for later on.]
   result = _manager->_system->getSpeakerMode( &_speakermode );
   fmod_audio_errcheck("_system->getSpeakerMode()", result);
 
-  VirtualFileSystem *vfs = VirtualFileSystem::get_global_ptr();
-  PT(VirtualFile) file = vfs->get_file(_file_name);
-  if (file == nullptr) {
-    // File not found.  We will display the appropriate error message below.
-    result = FMOD_ERR_FILE_NOTFOUND;
-
-  } else {
+  {
     bool preload = (fmod_audio_preload_threshold < 0) || (file->get_file_size() < fmod_audio_preload_threshold);
     int flags = FMOD_SOFTWARE;
     flags |= positional ? FMOD_3D : FMOD_2D;
@@ -149,7 +144,7 @@ FmodAudioSound(AudioManager *manager, Filename file_name, bool positional) {
 #if defined(HAVE_THREADS) && !defined(SIMPLE_THREADS)
       // Otherwise, if the Panda threading system is compiled in, we can
       // assign callbacks to read the file through the VFS.
-      name_or_data = (const char *)file.p();
+      name_or_data = (const char *)file;
       sound_info.length = (unsigned int)info.get_size();
       sound_info.useropen = open_callback;
       sound_info.userclose = close_callback;

panda/src/audiotraits/fmodAudioSound.h

@@ -70,10 +70,11 @@
 #include <fmod.hpp>
 #include <fmod_errors.h>
 
-class EXPCL_FMOD_AUDIO FmodAudioSound : public AudioSound {
- public:
+class VirtualFile;
 
-  FmodAudioSound(AudioManager *manager, Filename fn, bool positional );
+class EXPCL_FMOD_AUDIO FmodAudioSound : public AudioSound {
+public:
+  FmodAudioSound(AudioManager *manager, VirtualFile *file, bool positional);
   ~FmodAudioSound();
 
   // For best compatibility, set the loop_count, start_time, volume, and