lib/sound/openal_track.cpp: fix use-after-free pointed by gcc-15

[trofi]

gcc-15 detects use-after-free as:

lib/sound/openal_track.cpp: In function 'AUDIO_STREAM* sound_PlayStream(const char*, bool, float, const std::function<void(const AUDIO_STREAM*, const void*)>&, const void*)':
lib/sound/openal_track.cpp:1039:36: error: pointer used after 'void operator delete(void*, std::size_t)' [-Werror=use-after-free]
 1039 |                 alDeleteSources(1, &stream->source);
      |                                    ^~~~~~~~~~~~~~~
lib/sound/openal_track.cpp:1037:24: note: call to 'void operator delete(void*, std::size_t)' here
 1037 |                 delete stream;
      |                        ^~~~~~