Fix rare bug in the download queue

app/src/main/java/com/lagradost/cloudstream3/services/DownloadQueueService.kt

@@ -36,6 +36,7 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.debounce
 import kotlinx.coroutines.flow.takeWhile
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.flow.updateAndGet
@@ -186,6 +187,16 @@ class DownloadQueueService : Service() {
             debugAssert({ timeTaken == null }, { "Downloader startup should not time out" })
 
             totalDownloadFlow
+                .debounce { (instances, queue) ->
+                    // Filter away incorrect transient queue states.
+                    // For example when we pop the queue and add a download instance there exists a transient state where
+                    // there is no queue and no download instances (leading to an early exit)
+                    if (instances.isEmpty() && queue.isEmpty()) {
+                        500.milliseconds
+                    } else {
+                        0.milliseconds
+                    }
+                }
                 .takeWhile { (instances, queue) ->
                     // Stop if destroyed
                     isRunning