fixed bug in SearchPanel: could not be opened again, if it was closed before.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Search/SearchCommands.cs

@@ -71,7 +71,7 @@ namespace ICSharpCode.AvalonEdit.Search
 		
 		void ExecuteFind(object sender, ExecutedRoutedEventArgs e)
 		{
-			if (panel == null) {
+			if (panel == null || panel.IsClosed) {
 				panel = new SearchPanel();
 				panel.Attach(TextArea);
 			}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Search/SearchPanel.cs

@@ -323,6 +323,11 @@ namespace ICSharpCode.AvalonEdit.Search
 			}
 		}
 		
+		/// <summary>
+		/// Gets whether the Panel is already closed.
+		/// </summary>
+		public bool IsClosed { get; private set; }
+		
 		/// <summary>
 		/// Closes the SearchPanel.
 		/// </summary>
@@ -336,6 +341,8 @@ namespace ICSharpCode.AvalonEdit.Search
 			if (currentDocument != null)
 				currentDocument.TextChanged -= textArea_Document_TextChanged;
 			messageView.IsOpen = false;
+			textArea.Focus();
+			IsClosed = true;
 		}
 	}