Fix crash on torrent filenames in non-UTF-8 encoding (#4144)

macosx/NSDataAdditions.h

@@ -0,0 +1,15 @@
+// This file Copyright © 2022 Transmission authors and contributors.
+// It may be used under the MIT (SPDX: MIT) license.
+// License text can be found in the licenses/ folder.
+
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface NSData (NSDataAdditions)
+
+- (NSString*)hexString;
+
+@end
+
+NS_ASSUME_NONNULL_END