Core/Packets: converted SMSG_PLAY_MUSIC to packet class and corrected packet structure

src/server/game/Server/Packets/MiscPackets.cpp

@@ -154,3 +154,11 @@ WorldPacket const* WorldPackets::Misc::PlayObjectSound::Write()
 
     return &_worldPacket;
 }
+
+WorldPacket const* WorldPackets::Misc::PlayMusic::Write()
+{
+    _worldPacket << uint32(SoundKitID);
+    _worldPacket << SourceObjectGUID;
+
+    return &_worldPacket;
+}