Bug 1385402 - Cloud Storage API - Handle null while getting download folder r=Gijs

MozReview-Commit-ID: C9HC4KSAuG4

--HG--
extra : rebase_source : adb931f313e5ed33691eacd6bcd0312a8302f07c

toolkit/components/cloudstorage/CloudStorage.jsm

@@ -398,6 +398,7 @@ var CloudStorageInternal = {
    *        type of data downloaded, options are 'default', 'screenshot'
    *        default value is 'default'
    * @return {Promise} which resolves to full path to download folder
+   * Resolves null if a valid download folder is not found.
    */
   async getDownloadFolder(dataType = "default") {
     // Wait for cloudstorage to initialize if providers metadata is not available

toolkit/components/jsdownloads/src/DownloadIntegration.jsm

@@ -316,8 +316,8 @@ this.DownloadIntegration = {
       case 3: // Cloud Storage
         try {
           directoryPath = await CloudStorage.getDownloadFolder();
-        } catch(ex) {
-          // Either the preference isn't set or the directory cannot be created.
+        } catch(ex) {}
+        if (!directoryPath) {
           directoryPath = await this.getSystemDownloadsDirectory();
         }
         break;