Fix bug with undo after possible completions

repro is something like:

[ArrayL <Ctrl+Space> <Ctrl+Z> <Ctrl+Space> <Ctrl+Z>

Author: lzybkr

PSReadLine/Changes.txt

@@ -15,6 +15,7 @@ Bug fixes:
 * Event handlers that register for the engine event PowerShell.OnIdle should work now.
 * ClearScreen now just clears the visible screen, not the entire buffer.
 * Fix exception on error input during rendering after certain keywords like process, begin, or end.
+* Fix exception after undo from menu completion
 
 New functions:
 * ValidateAndAcceptLine

PSReadLine/Completion.cs

@@ -418,6 +418,7 @@ private void PossibleCompletionsImpl(CommandCompletion completions, bool menuSel
 
             if (menuSelect)
             {
+                RemoveEditsAfterUndo();
                 var undoPoint = _edits.Count;
 
                 int selectedItem = 0;

PSReadLine/UndoRedo.cs

@@ -6,14 +6,8 @@ namespace PSConsoleUtilities
 {
     public partial class PSConsoleReadLine
     {
-        private void SaveEditItem(EditItem editItem)
+        private void RemoveEditsAfterUndo()
         {
-            if (_statusIsErrorMessage)
-            {
-                // After an edit, clear the error message
-                ClearStatusMessage(render: true);
-            }
-
             // If there is some sort of edit after an undo, forget
             // any edit items that were undone.
             int removeCount = _edits.Count - _undoEditIndex;
@@ -26,6 +20,18 @@ private void SaveEditItem(EditItem editItem)
                     _editGroupStart -= removeCount;
                 }
             }
+        }
+
+        private void SaveEditItem(EditItem editItem)
+        {
+            if (_statusIsErrorMessage)
+            {
+                // After an edit, clear the error message
+                ClearStatusMessage(render: true);
+            }
+
+            RemoveEditsAfterUndo();
+
             _edits.Add(editItem);
             _undoEditIndex = _edits.Count;
         }
@@ -37,6 +43,8 @@ private void StartEditGroup()
                 // Nesting not supported.
                 throw new InvalidOperationException();
             }
+
+            RemoveEditsAfterUndo();
             _editGroupStart = _edits.Count;
         }