TagFile: add TagBuilder overload with ScanGenericTags() fallback

src/TagFile.hxx

@@ -24,6 +24,7 @@
 
 class Path;
 struct TagHandler;
+class TagBuilder;
 
 /**
  * Scan the tags of a song file.  Invokes matching decoder plugins,
@@ -35,4 +36,15 @@ struct TagHandler;
 bool
 tag_file_scan(Path path, const TagHandler &handler, void *handler_ctx);
 
+/**
+ * Scan the tags of a song file.  Invokes matching decoder plugins,
+ * and falls back to generic scanners (APE and ID3) if no tags were
+ * found (but the file was recognized).
+ *
+ * @return true if the file was recognized (even if no metadata was
+ * found)
+ */
+bool
+tag_file_scan(Path path, TagBuilder &builder);
+
 #endif