riched20: Add undo control state variable to ME_TextEditor.

dlls/riched20/editor.c

@@ -2973,6 +2973,7 @@ ME_TextEditor *ME_MakeEditor(ITextHost *texthost, BOOL bEmulateVersion10)
   ed->nUndoStackSize = 0;
   ed->nUndoLimit = STACK_SIZE_DEFAULT;
   ed->nUndoMode = umAddToUndo;
+  ed->undo_ctl_state = undoActive;
   ed->nParagraphs = 1;
   ed->nLastSelStart = ed->nLastSelEnd = 0;
   ed->last_sel_start_para = ed->last_sel_end_para = ed->pCursors[0].para;

dlls/riched20/editor.h

@@ -396,7 +396,7 @@ void ME_EmptyUndoStack(ME_TextEditor *editor) DECLSPEC_HIDDEN;
 
 static inline BOOL editor_undo_ignored(ME_TextEditor *editor)
 {
-    return editor->nUndoMode == umIgnore;
+    return editor->undo_ctl_state != undoActive || editor->nUndoMode == umIgnore;
 }
 
 /* txtsrv.c */

dlls/riched20/editstr.h

@@ -285,6 +285,12 @@ typedef enum {
   umAddBackToUndo
 } ME_UndoMode;
 
+typedef enum {
+  undoActive,
+  undoSuspended,
+  undoDisabled
+} ME_UndoControlState;
+
 enum undo_type
 {
     undo_insert_run,
@@ -402,6 +408,7 @@ typedef struct tagME_TextEditor
   int nUndoStackSize;
   int nUndoLimit;
   ME_UndoMode nUndoMode;
+  ME_UndoControlState undo_ctl_state;
   int nParagraphs;
   LONG nLastSelStart, nLastSelEnd;
   ME_Paragraph *last_sel_start_para, *last_sel_end_para;