Keep selection when going to drag feeds

Application/Options/FeedsOptionsPanel.xaml

@@ -28,7 +28,8 @@
                   CanUserResizeRows="False"
                   IsReadOnly="True"
                   HeadersVisibility="Column"
-                  Background="{x:Null}">
+                  Background="{x:Null}"
+                  PreviewMouseLeftButtonDown="HandleFeedListPreviewMouseLeftButtonDown">
             <DataGrid.Columns>
                 <DataGridTextColumn Binding="{Binding Name}"
                                     Header="{x:Static properties:Resources.FeedNameColumnHeader}"

Application/Options/FeedsOptionsPanel.xaml.cs

@@ -6,6 +6,7 @@ using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Data;
 using System.Windows.Input;
+using System.Windows.Media;
 using System.Xml;
 
 namespace FeedCenter.Options
@@ -433,5 +434,18 @@ namespace FeedCenter.Options
             var bulkFeedWindow = new BulkFeedWindow();
             bulkFeedWindow.Display(Window.GetWindow(this), Database);
         }
+
+        private void HandleFeedListPreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
+        {
+            // Get the object that was clicked on
+            var originalSource = (DependencyObject) e.OriginalSource;
+
+            // Look for a row that contains the object
+            var dataGridRow = (DataGridRow) FeedListBox.ContainerFromElement(originalSource);
+
+            // If the selection already contains this row then ignore it
+            if (dataGridRow != null && FeedListBox.SelectedItems.Contains(dataGridRow.Item))
+                e.Handled = true;
+        }
     }
 }