WM: avoid unnecessary undo step creation when duplicating

Calling duplicate operation without selecting anything registers an undo
step. If nothing is selected (keyframe, curve, object, etc.), cancel the
operator execution to prevent undo push.

Patch improves following operators:

- ACTION_OT_duplicate
- GPENCIL_OT_duplicate
- GRAPH_OT_duplicate
- MESH_OT_duplicate
- NODE_OT_duplicate
- OBJECT_OT_duplicate

Reviewed By: campbellbarton

Ref D14511

source/blender/editors/space_action/action_edit.c

@@ -878,11 +878,12 @@ void ACTION_OT_keyframe_insert(wmOperatorType *ot)
 
 /* ******************** Duplicate Keyframes Operator ************************* */
 
-static void duplicate_action_keys(bAnimContext *ac)
+static bool duplicate_action_keys(bAnimContext *ac)
 {
   ListBase anim_data = {NULL, NULL};
   bAnimListElem *ale;
   int filter;
+  bool changed = false;
 
   /* filter data */
   if (ELEM(ac->datatype, ANIMCONT_GPENCIL, ANIMCONT_MASK)) {
@@ -898,10 +899,11 @@ static void duplicate_action_keys(bAnimContext *ac)
   /* loop through filtered data and delete selected keys */
   for (ale = anim_data.first; ale; ale = ale->next) {
     if (ELEM(ale->type, ANIMTYPE_FCURVE, ANIMTYPE_NLACURVE)) {
-      duplicate_fcurve_keys((FCurve *)ale->key_data);
+      changed |= duplicate_fcurve_keys((FCurve *)ale->key_data);
     }
     else if (ale->type == ANIMTYPE_GPLAYER) {
       ED_gpencil_layer_frames_duplicate((bGPDlayer *)ale->data);
+      changed |= ED_gpencil_layer_frame_select_check((bGPDlayer *)ale->data);
     }
     else if (ale->type == ANIMTYPE_MASKLAYER) {
       ED_masklayer_frames_duplicate((MaskLayer *)ale->data);
@@ -915,6 +917,8 @@ static void duplicate_action_keys(bAnimContext *ac)
 
   ANIM_animdata_update(ac, &anim_data);
   ANIM_animdata_freelist(&anim_data);
+
+  return changed;
 }
 
 /* ------------------- */
@@ -929,7 +933,9 @@ static int actkeys_duplicate_exec(bContext *C, wmOperator *UNUSED(op))
   }
 
   /* duplicate keyframes */
-  duplicate_action_keys(&ac);
+  if (!duplicate_action_keys(&ac)) {
+    return OPERATOR_CANCELLED;
+  }
 
   /* set notifier that keyframes have changed */
   WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME | NA_ADDED, NULL);