Added comment why the return value is ignored.

Author: dlemstra

src/Magick.NET/MagickImageCollection.cs

@@ -1387,6 +1387,8 @@ public string ToBase64(IWriteDefines defines)
     public void TrimBounds()
     {
         using var imageAttacher = new TemporaryImageAttacher(_images);
+
+        // The return value is ignored because the return value always is IntPtr.Zero.
         _nativeInstance.Merge(_images[0], LayerMethod.Trimbounds);
     }