Fix DownloadService nullability

app/src/main/java/com/hippo/ehviewer/download/DownloadService.kt

@@ -87,7 +87,7 @@ class DownloadService : Service(), DownloadManager.DownloadListener {
         m509dBuilder = null
     }
 
-    override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
+    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
         handleIntent(intent)
         return START_STICKY
     }
@@ -408,7 +408,7 @@ class DownloadService : Service(), DownloadManager.DownloadListener {
 
     private fun checkStopSelf() {
         if (mDownloadManager == null || mDownloadManager!!.isIdle) {
-            stopForeground(true)
+            stopForeground(STOP_FOREGROUND_REMOVE)
             stopSelf()
         }
     }