Do not start Downloaders for failed downloads

In case there were failed chapter downloads in the queue the DownloadManager still created an Downloader and started it.
This Downloader would than immediately call "onComplete", since there is no available download, which then would refresh the Downloaders again which created an infinite loop until the failed download got removed from the queue

Author: schroda

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/download/DownloadManager.kt

@@ -28,7 +28,9 @@ import org.jetbrains.exposed.sql.select
 import org.jetbrains.exposed.sql.transactions.transaction
 import suwayomi.tachidesk.graphql.subscriptions.downloadSubscriptionSource
 import suwayomi.tachidesk.manga.impl.download.model.DownloadChapter
+import suwayomi.tachidesk.manga.impl.download.model.DownloadState
 import suwayomi.tachidesk.manga.impl.download.model.DownloadState.Downloading
+import suwayomi.tachidesk.manga.impl.download.model.DownloadState.Error
 import suwayomi.tachidesk.manga.impl.download.model.DownloadStatus
 import suwayomi.tachidesk.manga.impl.download.model.Status
 import suwayomi.tachidesk.manga.model.dataclass.ChapterDataClass
@@ -150,9 +152,12 @@ object DownloadManager {
         scope.launch {
             downloaderWatch.sample(1.seconds).collect {
                 val runningDownloaders = downloaders.values.filter { it.isActive }
-                logger.info { "Running: ${runningDownloaders.size}, Queued: ${downloadQueue.size}" }
+                val availableDownloads = downloadQueue.filter { it.state != Error }
+
+                logger.info { "Running: ${runningDownloaders.size}, Queued: ${downloadQueue.size}, Failed: ${downloadQueue.size - availableDownloads.size}" }
+
                 if (runningDownloaders.size < MAX_SOURCES_IN_PARAllEL) {
-                    downloadQueue.asSequence()
+                    availableDownloads.asSequence()
                         .map { it.manga.sourceId }
                         .distinct()
                         .minus(