Audio/Music: Fix Stop not resetting playing offset if music was already stopped

Also prevented a useless seek at destruction

include/Nazara/Audio/Music.hpp

@@ -73,6 +73,7 @@ namespace Nz
 
 			bool FillAndQueueBuffer(unsigned int buffer);
 			void MusicThread();
+			void StopThread();
 
 			static MusicLoader::LoaderList s_loaders;
 	};

src/Nazara/Audio/Music.cpp

@@ -91,7 +91,7 @@ namespace Nz
 	{
 		if (m_impl)
 		{
-			Stop();
+			StopThread();
 
 			delete m_impl;
 			m_impl = nullptr;
@@ -339,14 +339,9 @@ namespace Nz
 	{
 		NazaraAssert(m_impl, "Music not created");
 
-		if (m_impl->streaming)
-		{
-			m_impl->streaming = false;
-			m_impl->thread.Join();
-
+		StopThread();
 		SetPlayingOffset(0);
 	}
-	}
 
 	bool Music::FillAndQueueBuffer(unsigned int buffer)
 	{
@@ -444,5 +439,14 @@ namespace Nz
 		alDeleteBuffers(NAZARA_AUDIO_STREAMED_BUFFER_COUNT, buffers);
 	}
 
+	void Music::StopThread()
+	{
+		if (m_impl->streaming)
+		{
+			m_impl->streaming = false;
+			m_impl->thread.Join();
+		}
+	}
+
 	MusicLoader::LoaderList Music::s_loaders;
 }