Add validation for visible list prop (#429)

* Add validation for visible list prop

* Remove invalidated cookies

Author: georgiashay

src/components/Road.vue

@@ -117,7 +117,11 @@ export default {
   mounted () {
     const visibleList = JSON.parse(this.$cookies.get('visibleList' + this.roadID));
     if (this.$store.state.cookiesAllowed && visibleList) {
-      this.visibleList = visibleList;
+      if (Array.isArray(visibleList) && visibleList.length == this.numSems) {
+        this.visibleList = visibleList;
+      } else {
+        this.$cookies.remove('visibleList' + this.roadID);
+      }
     };
   }
 };