premature flac decode deletion solved

libflac-ffi.rkt

@@ -615,17 +615,16 @@
       (set! flac-file file)
       r))
 
+  ;;; Releases the decoder once; stopping after EOF or an earlier stop is safe.
   (define (delete)
-    (dbg-sound "flac-ffi 'delete")
-    (if (eq? fl #f)
-        (error "flac handler has already been deleted")
-        (begin
-          (FLAC__stream_decoder_finish fl)
-          (FLAC__stream_decoder_delete fl)
-          (set! fl #f)
-          ;; libFLAC cannot call the callbacks anymore after finish/delete,
-          ;; so the generated callback stubs can now be released.
-          (set-box! callback-keepers null))))
+    (when fl
+      (dbg-sound "flac-ffi 'delete")
+      (FLAC__stream_decoder_finish fl)
+      (FLAC__stream_decoder_delete fl)
+      (set! fl #f)
+      ;; libFLAC cannot call the callbacks anymore after finish/delete,
+      ;; so the generated callback stubs can now be released.
+      (set-box! callback-keepers null)))
 
   (define (process-single)
     (FLAC__stream_decoder_process_single fl))