Add missing test

ext/spl/tests/fixedarray_016.phpt

@@ -0,0 +1,20 @@
+--TEST--
+SPL: FixedArray: var_dump
+--FILE--
+<?php
+$a = new SplFixedArray(2);
+$a[0] = "foo";
+var_dump(empty($a[0]), empty($a[1]), $a);
+?>
+--EXPECTF--
+bool(false)
+bool(true)
+object(SplFixedArray)#1 (1) {
+  [u"array":u"SplFixedArray":private]=>
+  array(2) {
+    [0]=>
+    unicode(3) "foo"
+    [1]=>
+    NULL
+  }
+}