fix concurrent download (#7552)

* Fix concurrent download

* lower Concurrency

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

Co-authored-by: Vetle Ledaal <[email protected]>

Co-authored-by: Vetle Ledaal <[email protected]>
(cherry picked from commit b635f02d93502f1021f0fe87533dfd96d052ed2f)

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

@@ -341,8 +341,8 @@ class Downloader(
             // Get all the URLs to the source images, fetch pages if necessary
             .flatMap { download.source.fetchAllImageUrlsFromPageList(it) }
             // Start downloading images, consider we can have downloaded images already
-            // Concurrently do 5 pages at a time
-            .flatMap({ page -> getOrDownloadImage(page, download, tmpDir) }, 5)
+            // Concurrently do 2 pages at a time
+            .flatMap({ page -> getOrDownloadImage(page, download, tmpDir).subscribeOn(Schedulers.io()) }, 2)
             .onBackpressureLatest()
             // Do when page is downloaded.
             .doOnNext { notifier.onProgressChange(download) }