Index a finished download found on disk instead of downloading it again

app/src/main/java/eu/kanade/tachiyomi/data/download/Downloader.kt

@@ -393,6 +393,16 @@ class Downloader(
             download.chapter.scanlator,
             download.chapter.url,
         )
+
+        // Being stopped after the download is moved into place but before it's indexed leaves a finished download
+        // on disk that is still queued, and downloading it again would save a second copy next to it
+        if (mangaDir.findFile("$chapterDirname.cbz") != null || mangaDir.findFile(chapterDirname) != null) {
+            mangaDir.findFile(chapterDirname + TMP_DIR_SUFFIX)?.delete()
+            cache.addChapter(chapterDirname, mangaDir, download.manga)
+            download.status = Download.State.DOWNLOADED
+            return
+        }
+
         val tmpDir = mangaDir.createDirectory(chapterDirname + TMP_DIR_SUFFIX)!!
 
         try {