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/object/object_add.cc

@@ -3564,6 +3564,7 @@ static int duplicate_exec(bContext *C, wmOperator *op)
   ViewLayer *view_layer = CTX_data_view_layer(C);
   const bool linked = RNA_boolean_get(op->ptr, "linked");
   const eDupli_ID_Flags dupflag = (linked) ? (eDupli_ID_Flags)0 : (eDupli_ID_Flags)U.dupflag;
+  bool changed = false;
 
   /* We need to handle that here ourselves, because we may duplicate several objects, in which case
    * we also want to remap pointers between those... */
@@ -3582,6 +3583,7 @@ static int duplicate_exec(bContext *C, wmOperator *op)
      * the list is made in advance */
     ED_object_base_select(base, BA_DESELECT);
     ED_object_base_select(basen, BA_SELECT);
+    changed = true;
 
     if (basen == nullptr) {
       continue;
@@ -3598,6 +3600,10 @@ static int duplicate_exec(bContext *C, wmOperator *op)
   }
   CTX_DATA_END;
 
+  if (!changed) {
+    return OPERATOR_CANCELLED;
+  }
+
   /* Note that this will also clear newid pointers and tags. */
   copy_object_set_idnew(C);