Fixed null reference exception in project browser if the last selected file is null.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/trunk@1028 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Gui/Pads/ProjectBrowser/ProjectBrowserControl.cs

@@ -343,7 +343,9 @@ namespace ICSharpCode.SharpDevelop.Project
 		
 		void TreeViewAfterExpand(object sender, TreeViewEventArgs e)
 		{ // attempt to restore the last selection if its path has been reexpanded
-			SelectFile(lastSelectionTarget);
+			if (lastSelectionTarget != null) {
+				SelectFile(lastSelectionTarget);
+			}
 		}
 		
 		void TreeViewBeforeSelect(object sender, TreeViewCancelEventArgs e)