Add OIIO_NODISCARD_ERROR to ImageInput::valid_file

Author: PandorasPalette

src/include/OpenImageIO/imageio.h

@@ -1143,10 +1143,10 @@ class OIIO_API ImageInput {
     ///
     /// @returns
     ///         `true` upon success, or `false` upon failure.
-    virtual bool valid_file (const std::string& filename) const;
+    OIIO_NODISCARD_ERROR virtual bool valid_file (const std::string& filename) const;
 
     /// Check valid file using a UTF-16 encoded wstring filename.
-    bool valid_file (const std::wstring& filename) const {
+    OIIO_NODISCARD_ERROR bool valid_file (const std::wstring& filename) const {
         return valid_file(Strutil::utf16_to_utf8(filename));
     }