fix:修复u-image组件的src先传入空值再传入非空值后, 无法触发loading效果的bug

uview-ui/components/u-image/u-image.vue

@@ -172,6 +172,7 @@ export default {
 					this.loading = false;
 				} else {
 					this.isError = false;
+          this.loading = true;
 				}
 			}
 		}