show indeterminate download, if we don't know the file size. better naming of download command

NextcloudApp/Strings/en-US/Resources.resw

@@ -365,4 +365,10 @@ Would you like to inform the application developers and submit the prepared erro
   <data name="ServerWithGivenAddressIsNotReachable" xml:space="preserve">
     <value>The server with the address {0} is not reachable.</value>
   </data>
+  <data name="DownloadAsZip.Text" xml:space="preserve">
+    <value>Download as ZIP file</value>
+  </data>
+  <data name="DownloadingFileProgressIndeterminate" xml:space="preserve">
+    <value>{0} downloaded</value>
+  </data>
 </root>

NextcloudApp/ViewModels/SingleFileDownloadPageViewModel.cs

@@ -32,6 +32,7 @@ namespace NextcloudApp.ViewModels
         private ResourceInfo _resourceInfo;
         private string _downloadingFileProgressText;
         private StorageFile _currentFile;
+        private bool _isIndeterminate;
 
         public SingleFileDownloadPageViewModel(INavigationService navigationService, IResourceLoader resourceLoader)
         {
@@ -146,6 +147,12 @@ namespace NextcloudApp.ViewModels
                 BytesDownloaded = (int)progressInfo.BytesReceived;
             });
         }
+        
+        public bool IsIndeterminate
+        {
+            get { return _isIndeterminate; }
+            private set { SetProperty(ref _isIndeterminate, value); }
+        }
 
         public int PercentageDownloaded
         {
@@ -191,15 +198,24 @@ namespace NextcloudApp.ViewModels
 
         private void Update()
         {
+            if (BytesTotal == 0)
+            {
+                IsIndeterminate = true;
+                DownloadingFileProgressText = string.Format(
+                    _resourceLoader.GetString("DownloadingFileProgressIndeterminate"),
+                    _converter.Convert((long)BytesDownloaded, typeof(string), null, CultureInfo.CurrentCulture.ToString())
+                );
+                return;
+            }
+
             var percentage = (double)BytesDownloaded / BytesTotal;
             PercentageDownloaded = (int)(percentage * 100);
 
+            IsIndeterminate = false;
             DownloadingFileProgressText = string.Format(
-            _resourceLoader.GetString("DownloadingFileProgress"),
-            _converter.Convert((long)BytesDownloaded, typeof(string), null,
-                CultureInfo.CurrentCulture.ToString()),
-            _converter.Convert(BytesTotal, typeof(string), null,
-                CultureInfo.CurrentCulture.ToString())
+                _resourceLoader.GetString("DownloadingFileProgress"),
+                _converter.Convert((long)BytesDownloaded, typeof(string), null, CultureInfo.CurrentCulture.ToString()),
+                _converter.Convert(BytesTotal, typeof(string), null, CultureInfo.CurrentCulture.ToString())
             );
         }
     }

NextcloudApp/Views/DirectoryListPage.xaml

@@ -266,8 +266,8 @@
                                             Style="{StaticResource MenuFlyoutIconItemStyle}"/>
                                         <MenuFlyoutItem 
                                             Tag="Download"
-                                            x:Uid="Download"
-                                            Text="Download"
+                                            x:Uid="DownloadAsZip"
+                                            Text="Download as ZIP file"
                                             Command="{Binding DataContext.DownloadResourceCommand, ElementName=Page}"
                                             CommandParameter="{Binding}"
                                             Style="{StaticResource MenuFlyoutIconItemStyle}"/>

NextcloudApp/Views/SingleFileDownloadPage.xaml

@@ -21,7 +21,8 @@
             <ProgressBar 
                 Minimum="0"
                 Value="{Binding PercentageDownloaded}"
-                Maximum="100"/>
+                Maximum="100"
+                IsIndeterminate="{Binding IsIndeterminate}"/>
             <TextBlock 
                 Text="{Binding DownloadingFileProgressText}"
                 HorizontalAlignment="Right"