tsk-83: Add None value for MusicTypes and CoverArtTypes (#87)

Closes #83

Reviewed-on: #87
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

src/types.rs

@@ -4,6 +4,7 @@ pub enum MusicTypes {
     WavExtension,
     FlacExtension,
     MPThreeExtension,
+    None,
 }
 
 #[derive(Debug)]
@@ -11,4 +12,5 @@ pub enum CoverArtTypes {
     PngExtension,
     JpegExtension,
     JpgExtension,
+    None,
 }