Fix loading a file saved w/ dyntopo

Ensure ED_editors_init doesn't create any undo steps
before the initial memfile undo is written.

source/blender/editors/sculpt_paint/sculpt.c

@@ -5739,11 +5739,18 @@ void ED_object_sculptmode_enter_ex(
 		}
 
 		if (message_unsupported == NULL) {
+			/* Needed because we may be entering this mode before the undo system loads. */
+			wmWindowManager *wm = bmain->wm.first;
+			bool has_undo = wm->undo_stack != NULL;
 			/* undo push is needed to prevent memory leak */
-			sculpt_undo_push_begin("Dynamic topology enable");
+			if (has_undo) {
+				sculpt_undo_push_begin("Dynamic topology enable");
+			}
 			sculpt_dynamic_topology_enable_ex(depsgraph, scene, ob);
-			sculpt_undo_push_node(ob, NULL, SCULPT_UNDO_DYNTOPO_BEGIN);
-			sculpt_undo_push_end();
+			if (has_undo) {
+				sculpt_undo_push_node(ob, NULL, SCULPT_UNDO_DYNTOPO_BEGIN);
+				sculpt_undo_push_end();
+			}
 		}
 		else {
 			BKE_reportf(reports, RPT_WARNING,

source/blender/editors/util/ed_util.c

@@ -95,16 +95,15 @@ void ED_editors_init(bContext *C)
 	Scene *scene = CTX_data_scene(C);
 	wmWindowManager *wm = CTX_wm_manager(C);
 
-	if (wm->undo_stack == NULL) {
-		wm->undo_stack = BKE_undosys_stack_create();
-	}
-
 	/* This is called during initialization, so we don't want to store any reports */
 	ReportList *reports = CTX_wm_reports(C);
 	int reports_flag_prev = reports->flag & ~RPT_STORE;
 
 	SWAP(int, reports->flag, reports_flag_prev);
 
+	/* Don't do undo pushes when calling an operator. */
+	wm->op_undo_depth++;
+
 	/* toggle on modes for objects that were saved with these enabled. for
 	 * e.g. linked objects we have to ensure that they are actually the
 	 * active object in this scene. */
@@ -177,6 +176,7 @@ void ED_editors_init(bContext *C)
 	}
 
 	SWAP(int, reports->flag, reports_flag_prev);
+	wm->op_undo_depth--;
 }
 
 /* frees all editmode stuff */