Fix SoundPlayer handling of partial reads on streams (#82612)

SoundPlayer assumes that a Read on a stream will return everything asked for, and that's not the case.

Author: stephentoub

src/libraries/System.Windows.Extensions/src/System/Media/SoundPlayer.cs

@@ -310,7 +310,20 @@ private void LoadStream(bool loadSync)
                 int streamLen = (int)_stream.Length;
                 _currentPos = 0;
                 _streamData = new byte[streamLen];
-                _stream.Read(_streamData, 0, streamLen);
+#if NET7_0_OR_GREATER
+                _stream.ReadExactly(_streamData);
+#else
+                int totalRead = 0;
+                while (totalRead < streamLen)
+                {
+                    int bytesRead = _stream.Read(_streamData, totalRead, streamLen - totalRead);
+                    if (bytesRead <= 0)
+                    {
+                        throw new EndOfStreamException();
+                    }
+                    totalRead += bytesRead;
+                }
+#endif
                 IsLoadCompleted = true;
                 OnLoadCompleted(new AsyncCompletedEventArgs(null, false, null));
             }

src/libraries/System.Windows.Extensions/tests/System/Media/SoundPlayerTests.cs

@@ -293,6 +293,22 @@ public void PlayLooping_NullStream_Success()
             player.PlayLooping();
         }
 
+        [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsSoundPlaySupported))]
+        [MemberData(nameof(Play_String_TestData))]
+        [OuterLoop]
+        public void PlaySync_TrickledData_Success(string sourceLocation)
+        {
+            using var player = new SoundPlayer();
+            player.Stream = new TrickleStream(File.ReadAllBytes(sourceLocation.Replace("file://", "")));
+            player.PlaySync();
+        }
+
+        private sealed class TrickleStream : MemoryStream
+        {
+            public TrickleStream(byte[] bytes) : base(bytes) { }
+            public override int Read(byte[] buffer, int offset, int count) => base.Read(buffer, offset, Math.Min(count, 1));
+        }
+
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsSoundPlaySupported))]
         [OuterLoop]
         public void PlaySync_NullStream_Success()