Make torchvision.io.read_image{,_async} and torchvision.io.read_async allow subsequent opening of the file for reading (#1495)

* Fix torchvision.io.read_image{,_async}.

Addressed to #1494.

* Update src/TorchVision/IO/Image.cs.
  + Fix torchvision.io.read_image{,_async}.
    - Allow subsequent opening of the file for reading.

* Fix torchvision.io.read_file_async.

* Update src/TorchVision/File.cs.
  + Fix torchvision.io.read_file_async.
    - Allow subsequent opening of the file for reading.

---------

Co-authored-by: Masaru Kimura <masaru@hacarus.com>

Author: hiyuh

src/TorchVision/File.cs

@@ -33,7 +33,7 @@ public static async Task<Tensor> read_file_async(string filename)
             {
                 byte[] data;
 
-                using (FileStream stream = File.Open(filename, FileMode.Open)) {
+                using (FileStream stream = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.Read)) {
                     data = new byte[stream.Length];
                     await stream.ReadAsync(data, 0, data.Length);
                 }

src/TorchVision/IO/Image.cs

@@ -136,7 +136,7 @@ public enum ImageReadMode
             /// </returns>
             public static Tensor read_image(string filename, ImageReadMode mode = ImageReadMode.UNCHANGED, Imager imager = null)
             {
-                using (FileStream stream = File.Open(filename, FileMode.Open))
+                using (FileStream stream = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
                     return (imager ?? DefaultImager).DecodeImage(stream, mode);
             }
 
@@ -167,7 +167,7 @@ public static Tensor read_image(Stream stream, ImageReadMode mode = ImageReadMod
             public static async Task<Tensor> read_image_async(string filename, ImageReadMode mode = ImageReadMode.UNCHANGED, Imager imager = null)
             {
 
-                using (FileStream stream = File.Open(filename, FileMode.Open))
+                using (FileStream stream = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.Read))
                     return await (imager ?? DefaultImager).DecodeImageAsync(stream, mode);
             }