feat: 优化填充组图层背景命令，重构填充对象创建逻辑

src/component/Canvas/CanvasEditor/commands/FillGroupLayerBackgroundCommand.js

@@ -123,6 +123,21 @@ export class FillGroupLayerBackgroundCommand extends Command {
           scaleX: clippingMaskFabricObject.scaleX || 1,
           scaleY: clippingMaskFabricObject.scaleY || 1,
         });
+      } else {
+        this.newFill = new fabric.Rect({
+          width: this.canvasManager?.canvasWidth?.value || this.canvas.width,
+          height: this.canvasManager?.canvasHeight?.value || this.canvas.height,
+          left: this.canvas.width / 2 || 0,
+          top: this.canvas.height / 2 || 0,
+          fill: this.fillColor,
+          layerId: this.layerId,
+          id: this.oldFill?.id || generateId("fill-"),
+          selectable: false,
+          evented: false,
+          originX: "center",
+          originY: "center",
+        });
+      }
       this.newFill.clipPath = clippingMaskFabricObject; // 设置填充的遮罩
       this.newFill.dirty = true; // 标记为脏，以便重新
       this.canvas.add(this.newFill);
@@ -144,8 +159,6 @@ export class FillGroupLayerBackgroundCommand extends Command {
       this.canvasManager.thumbnailManager?.generateLayerThumbnail(
         this.layer.id
       );
-      }
-
       return false;
     }
     const canvasObj = findObjectById(this.canvas, firstObj?.id)?.object;