retry download workers on resume

core/src/main/groovy/com/muwire/core/download/Downloader.groovy

@@ -156,7 +156,13 @@ public class Downloader {
     }
     
     public void resume() {
-        downloadManager.resume(this)
+        activeWorkers.each { destination, worker ->
+            if (worker.currentState == WorkerState.FINISHED) {
+                def newWorker = new DownloadWorker(destination)
+                activeWorkers.put(destination, newWorker)
+                executorService.submit(newWorker)
+            }
+        }
     }
     
     class DownloadWorker implements Runnable {

gui/griffon-app/models/com/muwire/gui/MainFrameModel.groovy

@@ -110,7 +110,9 @@ class MainFrameModel {
                         lastRetryTime = now
                         runInsideUIAsync {
                             downloads.each {
-                                if (it.downloader.currentState == Downloader.DownloadState.FAILED)
+                                def state = it.downloader.currentState
+                                if (state == Downloader.DownloadState.FAILED || 
+                                    state == Downloader.DownloadState.DOWNLOADING)
                                     it.downloader.resume()
                                 updateTablePreservingSelection("downloads-table")
                             }