Breadcrumb: fix regression of dynamic `to` support (#11286)

packages/breadcrumb/src/breadcrumb-item.vue

@@ -29,15 +29,13 @@
     mounted() {
       this.separator = this.elBreadcrumb.separator;
       this.separatorClass = this.elBreadcrumb.separatorClass;
-      if (this.to) {
-        let link = this.$refs.link;
-        let to = this.to;
+      const link = this.$refs.link;
       link.setAttribute('role', 'link');
       link.addEventListener('click', _ => {
-          this.replace ? this.$router.replace(to)
-            : this.$router.push(to);
+        const { to, $router } = this;
+        if (!to || !$router) return;
+        this.replace ? $router.replace(to) : $router.push(to);
       });
     }
-    }
   };
 </script>