pull: keep self-prefixed multi-orig components in place

A component tarball whose entries already carry the addon prefix
('www/...' in sqlite3's 'sqlite3_3.53.4.orig-www.tar.xz') extracts
to its end state, but the wrapper detection named it a wrapper and
unwrap_into then cleared the addon target - destroying the component
just extracted into it - and unwrapped the emptied directory into
itself: no 'www' at all, and the deb failed at dh_installdocs over
the missing 'www/*' docs.

dpkg-source unpacks a component into '<root>/<addon>': when the
tarball's own layout already is that, the extraction is the end
state; leave it alone.

src/pull.rs

@@ -167,18 +167,23 @@ fn component_addon(name: &str) -> Option<&str> {
 /// `dir/<addon>` for a multi-orig component, replacing any pre-existing
 /// addon directory.
 fn unwrap_into(dir: &Path, wrapper: &Path, addon: Option<&str>) -> Result<(), Box<dyn Error>> {
-    let target = match addon {
+    match addon {
+        // dpkg-source unpacks a component into '<root>/<addon>': a tarball
+        // whose entries already carry that prefix ('www/...' in
+        // 'sqlite3_3.53.4.orig-www.tar.xz') extracts to its end state, and
+        // unwrapping it would clear the target and move the cleared
+        // directory into itself.
+        Some(addon) if wrapper.file_name().is_some_and(|name| name == addon) => Ok(()),
         Some(addon) => {
             let target = dir.join(addon);
             if target.is_dir() {
                 std::fs::remove_dir_all(&target)?;
             }
             std::fs::create_dir_all(&target)?;
-            target
+            unwrap_wrapper(&target, wrapper)
         }
-        None => dir.to_path_buf(),
+        None => unwrap_wrapper(dir, wrapper),
-    };
+    }
-    unwrap_wrapper(&target, wrapper)
 }
 
 /// Move the contents of an archive's wrapper directory up into `dir` itself.
@@ -1450,6 +1455,41 @@ mod tests {
         assert!(!tree.join("dovecot-pigeonhole-2.4.5").exists());
     }
 
+    #[test]
+    fn test_unwrap_component_already_prefixed_with_addon() {
+        // Regression: a component tarball whose entries already carry the
+        // addon prefix ('www/...' in 'sqlite3_3.53.4.orig-www.tar.xz')
+        // extracts to its end state. It used to be treated as a wrapper of
+        // the same name as the addon: unwrap_into cleared the target —
+        // destroying the component just extracted into it — and unwrapped
+        // the emptied directory into itself, leaving no 'www' at all.
+        let temp_dir = tempfile::tempdir().unwrap();
+        let tar_path = temp_dir.path().join("pkg_1.0.orig-www.tar.gz");
+        std::fs::write(
+            &tar_path,
+            build_tar(&[("www/README", b"docs"), ("www/img/x", b"img")]),
+        )
+        .unwrap();
+
+        let tree = temp_dir.path().join("tree");
+        let extracted = extract_tar_archive(&tar_path, &tree, None, |f| f).unwrap();
+        unwrap_into(
+            &tree,
+            &extracted.wrapper.unwrap(),
+            component_addon("pkg_1.0.orig-www.tar.gz"),
+        )
+        .unwrap();
+
+        assert_eq!(
+            std::fs::read_to_string(tree.join("www/README")).unwrap(),
+            "docs"
+        );
+        assert_eq!(
+            std::fs::read_to_string(tree.join("www/img/x")).unwrap(),
+            "img"
+        );
+    }
+
     /// A minimal ustar archive of `pkg-1.0/{Makefile,doc/readme}`,
     /// bz2-compressed.
     const BZ2_TAR_WRAPPED: &[u8] = &[