Cleanup: break before the default case in switch statements

While missing the break before a default that only breaks isn't
an error, it means adding new cases needs to remember to add the
break for an existing case, changing the default case will also
result in an unintended fall-through.

Also avoid `default:;` and add an explicit break.

source/blender/blenkernel/intern/attribute.cc

@@ -421,6 +421,7 @@ int BKE_id_attribute_data_length(ID *id, CustomDataLayer *layer)
       if (mesh->edit_mesh != nullptr) {
         return 0;
       }
+      break;
     }
     default:
       break;

source/blender/depsgraph/intern/eval/deg_eval_runtime_backup.cc

@@ -62,6 +62,7 @@ void RuntimeBackup::init_from_id(ID *id)
       break;
     case ID_GD:
       gpencil_backup.init_from_gpencil(reinterpret_cast<bGPdata *>(id));
+      break;
     default:
       break;
   }
@@ -104,6 +105,7 @@ void RuntimeBackup::restore_to_id(ID *id)
       break;
     case ID_GD:
       gpencil_backup.restore_to_gpencil(reinterpret_cast<bGPdata *>(id));
+      break;
     default:
       break;
   }

source/blender/editors/interface/interface.cc

@@ -6754,10 +6754,11 @@ void UI_but_extra_icon_string_info_get(struct bContext *C, uiButExtraOpIcon *ext
         if (ui_but_extra_icon_event_operator_string(C, extra_icon, buf, sizeof(buf))) {
           tmp = BLI_strdup(buf);
         }
+        break;
       }
+      default:
         /* Other types not supported. The caller should expect that outcome, no need to message or
          * assert here. */
-      default:
         break;
     }
 

source/blender/editors/interface/interface_template_search_menu.cc

@@ -918,6 +918,7 @@ static void menu_search_arg_free_fn(void *data_v)
           WM_operator_properties_free(item->op.opptr);
           MEM_freeN(item->op.opptr);
         }
+        break;
       }
       case MenuSearch_Item::Type::RNA: {
         break;

source/blender/editors/object/object_vgroup.cc

@@ -1773,7 +1773,8 @@ static void vgroup_lock_all(Object *ob, int action, int mask)
             continue;
           }
           break;
-        default:;
+        default:
+          break;
       }
 
       if (dg->flag & DG_LOCK_WEIGHT) {
@@ -1795,7 +1796,8 @@ static void vgroup_lock_all(Object *ob, int action, int mask)
           continue;
         }
         break;
-      default:;
+      default:
+        break;
     }
 
     switch (action) {

source/blender/modifiers/intern/MOD_nodes.cc

@@ -297,6 +297,7 @@ static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphConte
       case ID_IM:
       case ID_TE: {
         DEG_add_generic_id_relation(ctx->node, id, "Nodes Modifier");
+        break;
       }
       default: {
         /* Purposefully don't add relations for materials. While there are material sockets,

source/blender/windowmanager/intern/wm_event_system.cc

@@ -1591,6 +1591,7 @@ static int wm_operator_call_internal(bContext *C,
         case WM_OP_EXEC_AREA:
         case WM_OP_EXEC_SCREEN:
           event = nullptr;
+          break;
         default:
           break;
       }