Add property to get the number of a page

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

@@ -302,7 +302,7 @@ class Downloader(private val context: Context, private val provider: DownloadPro
         if (page.imageUrl == null)
             return Observable.just(page)
 
-        val filename = String.format("%03d", page.index + 1)
+        val filename = String.format("%03d", page.number)
         val tmpFile = tmpDir.findFile("$filename.tmp")
 
         // Delete temp file if it exists.

app/src/main/java/eu/kanade/tachiyomi/data/source/model/Page.kt

@@ -12,6 +12,9 @@ class Page(
         @Transient var uri: Uri? = null
 ) : ProgressListener {
 
+    val number: Int
+        get() = index + 1
+
     @Transient lateinit var chapter: ReaderChapter
 
     @Transient @Volatile var status: Int = 0