Fix duplicate images after resuming paused downloads (#3504)

Co-authored-by: AntsyLich <59261191+AntsyLich@users.noreply.github.com>

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

@@ -439,9 +439,7 @@ class Downloader(
 
         // Try to find the image file
         val imageFile = tmpDir.listFiles()?.firstOrNull {
-            val filename = it.name
-            if (filename == null || filename.endsWith(".tmp")) return@firstOrNull false
-            filename.startsWith("$filename.") || filename.startsWith("${filename}__001")
+            isDownloadedPageImage(it.name ?: return@firstOrNull false, filename)
         }
 
         try {
@@ -601,6 +599,16 @@ class Downloader(
         return downloadedImagesCount == downloadPageCount
     }
 
+    /**
+     * Checks if the file name matches a downloaded page image.
+     *
+     * @param fileName Name of the file to check
+     * @param pagePrefix Expected page prefix (e.g., "001")
+     */
+    private fun isDownloadedPageImage(fileName: String, pagePrefix: String): Boolean =
+        !fileName.endsWith(".tmp") || fileName.startsWith("$pagePrefix.") ||
+            fileName.startsWith("${pagePrefix}__001.")
+
     /**
      * Archive the chapter pages as a CBZ.
      */