Remove Hidden Information keeps an unlink that was its only removal

Unlinking images nothing draws ran before the check for an empty result,
so a run where it was the only removal returned NothingToApply. The
remove-hidden edit and the Action Wizard step then dropped the working
copy, and the image stayed in the file. A run that unlinked anything now
succeeds and asks for the full rewrite.

crates/redact/src/sanitize.rs

@@ -672,9 +672,9 @@ pub fn remove_hidden(doc: &mut Document, which: &[Hidden]) -> Result<Vec<(Hidden
         }
     }
     // Images taken off their page (Delete Image, Replace Image) are still listed in its
-    // resources: the full rewrite would keep them.
-    crate::interp::unlink_undrawn(doc)?;
-    if done.is_empty() {
+    // resources: the full rewrite would keep them. Unlinking them is a removal of its own.
+    let unlinked = crate::interp::unlink_undrawn(doc)?;
+    if done.is_empty() && unlinked == 0 {
         return Err(RedactError::NothingToApply);
     }
     // The rewrite drops the revisions that held the removed content, so it is a different file from

crates/redact/src/tests.rs

@@ -4253,6 +4253,22 @@ fn images_no_page_draws_leave_with_hidden_information() {
     }
 }
 
+/// Unlinking an image nothing draws is a removal of its own: with nothing else to remove, it is
+/// still applied, not reported as nothing to do.
+#[test]
+fn unlinking_alone_still_applies() {
+    use crate::sanitize::{Hidden, remove_hidden};
+    let mut doc = pdf(vec![
+        b"<< /Type /Catalog /Pages 2 0 R >>".to_vec(),
+        b"<< /Type /Pages /Kids [3 0 R] /Count 1 >>".to_vec(),
+        b"<< /Type /Page /Parent 2 0 R /MediaBox [0 0 300 300] /Resources << /XObject << /Deleted 4 0 R >> >> >>".to_vec(),
+        gray_image(b"DELETEDIMAGEBYTES"),
+    ]);
+    assert_eq!(remove_hidden(&mut doc, &[Hidden::Metadata]), Ok(Vec::new()));
+    let bytes = write_full(&doc, &SaveOptions { object_streams: false, ..SaveOptions::default() }).unwrap();
+    assert!(!bytes.windows(17).any(|w| w == b"DELETEDIMAGEBYTES"), "the deleted image survived the save");
+}
+
 /// A name a pattern, a form, an appearance or a soft mask doesn't define is looked up in the
 /// page's resources, /Resources of its own or not: an image drawn only that way is still shown,
 /// so it stays. One no content names goes.