Avoid inexact read with 'Stream.Read' (#6847)

src/Ryujinx.Gtk3/UI/Windows/AvatarWindow.cs

@@ -233,7 +233,7 @@ namespace Ryujinx.UI.Windows
             reader.ReadInt64(); // Padding
 
             byte[] input = new byte[stream.Length - stream.Position];
-            stream.Read(input, 0, input.Length);
+            stream.ReadExactly(input, 0, input.Length);
 
             long inputOffset = 0;