Ensure shortcut fusion works for _.at with no indexes specified.

lodash.js

@@ -13895,8 +13895,11 @@
 
     LazyWrapper.prototype.at = rest(function(paths) {
       paths = baseFlatten(paths);
-      return (paths.length == 1 && isIndex(paths[0]))
-        ? this.slice(paths[0], +paths[0] + 1)
+      var length = paths.length,
+          start = length ? paths[0] : 0;
+
+      return (length < 2 && isIndex(start))
+        ? this.slice(start, length ? (+start + 1) : start)
         : new LazyWrapper(this);
     });