Add tests for json_decode with depth below 0

Author: ntzm

ext/json/tests/json_decode_error.phpt

@@ -13,6 +13,9 @@ echo "\n-- Testing json_decode() function with more than expected no. of argumen
 $extra_arg = 10;
 var_dump(json_decode('"abc"', true, 512, 0, $extra_arg));
 
+echo "\n-- Testing json_decode() function with depth below 0 --\n";
+var_dump(json_decode('"abc"', true, -1));
+
 ?>
 ===Done===
 --EXPECTF--
@@ -27,4 +30,9 @@ NULL
 
 Warning: json_decode() expects at most 4 parameters, 5 given in %s on line %d
 NULL
+
+-- Testing json_decode() function with depth below 0 --
+
+Warning: json_decode(): Depth must be greater than zero in %s on line %d
+NULL
 ===Done===