优化

modules/book/src/main/java/me/ag2s/epublib/domain/MediaTypes.java

@@ -53,10 +53,11 @@ public class MediaTypes {
             "application/adobe-page-template+xml", ".xpgt");
     public static final MediaType PLS = new MediaType("application/pls+xml",
             ".pls");
+    public static final MediaType UNKNOWN = new MediaType("application/octet-stream", "");
 
     public static final MediaType[] mediaTypes = new MediaType[]{
             XHTML, EPUB, JPG, PNG, GIF, CSS, SVG, TTF, NCX, XPGT, OPENTYPE, WOFF,
-            SMIL, PLS, JAVASCRIPT, MP3, MP4, OGG
+            SMIL, PLS, JAVASCRIPT, MP3, MP4, OGG, UNKNOWN
     };
 
     public static final Map<String, MediaType> mediaTypesByName = new HashMap<>();