Media: Internally keep a reference to the last set Media

libvlc_media_player_get_media increments the ref count of the media, which may easily
cause a memory leak, as this is very unusual behavior for C# property getter to
have these types of consequences. Users don't have the reflex to dispose every Media returned
by the getter property.

Holding a ref internally in the mediaplayer prevents from incrementing the native ref count
of the media object.

https://code.videolan.org/videolan/LibVLCSharp/-/issues/442

Author: mfkl

src/LibVLCSharp/Shared/MediaPlayer.cs

@@ -34,11 +34,6 @@ readonly struct Native
             internal static extern void LibVLCMediaPlayerSetMedia(IntPtr mediaPlayer, IntPtr media);
 
 
-            [DllImport(Constants.LibraryName, CallingConvention = CallingConvention.Cdecl,
-                EntryPoint = "libvlc_media_player_get_media")]
-            internal static extern IntPtr LibVLCMediaPlayerGetMedia(IntPtr mediaPlayer);
-
-
             [DllImport(Constants.LibraryName, CallingConvention = CallingConvention.Cdecl,
                 EntryPoint = "libvlc_media_player_event_manager")]
             internal static extern IntPtr LibVLCMediaPlayerEventManager(IntPtr mediaPlayer);
@@ -623,8 +618,11 @@ public MediaPlayer(Media media)
             : base(() => Native.LibVLCMediaPlayerNewFromMedia(media.NativeReference), Native.LibVLCMediaPlayerRelease)
         {
             _gcHandle = GCHandle.Alloc(this);
+            _media = media;
         }
 
+        Media? _media;
+
         /// <summary>
         /// Get the media used by the media_player.
         /// Set the media that will be used by the media_player.
@@ -635,10 +633,19 @@ public Media? Media
         {
             get
             {
-                var mediaPtr = Native.LibVLCMediaPlayerGetMedia(NativeReference);
-                return mediaPtr == IntPtr.Zero ? null : new Media(mediaPtr);
+                return _media;
+            }
+            set
+            {
+                if(_media?.NativeReference != IntPtr.Zero)
+                {
+                    _media?.Dispose();
+                    _media = null;
+                }
+
+                _media = value;
+                Native.LibVLCMediaPlayerSetMedia(NativeReference, value?.NativeReference ?? IntPtr.Zero);
             }
-            set => Native.LibVLCMediaPlayerSetMedia(NativeReference, value?.NativeReference ?? IntPtr.Zero);
         }
 
         /// <summary>
@@ -2408,6 +2415,11 @@ protected override void Dispose(bool disposing)
             {
                 if (_gcHandle.IsAllocated)
                     _gcHandle.Free();
+                if (_media?.NativeReference != IntPtr.Zero)
+                {
+                    _media?.Dispose();
+                    _media = null;
+                }    
             }
 
             base.Dispose(disposing);