Fixed exception when deleting a file that had multiple view contents open in the same WorkbenchWindow (e.g. Source view+Designer view, or Source view+Subversion History).

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@2693 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Gui/Workbench/DefaultWorkbench.cs

@@ -459,7 +459,12 @@ namespace ICSharpCode.SharpDevelop.Gui
 			foreach (OpenedFile file in FileService.OpenedFiles) {
 				if (FileUtility.IsBaseDirectory(e.FileName, file.FileName)) {
 					foreach (IViewContent content in file.RegisteredViewContents.ToArray()) {
-						content.WorkbenchWindow.CloseWindow(true);
+						// content.WorkbenchWindow can be null if multiple view contents
+						// were in the same WorkbenchWindow and both should be closed
+						// (e.g. Windows Forms Designer, Subversion History View)
+						if (content.WorkbenchWindow != null) {
+							content.WorkbenchWindow.CloseWindow(true);
+						}
 					}
 				}
 			}