Fix compile error using zend_parse_parameters_throw()

Fix compile error using zend_parse_parameters_throw()

Fixes a bug introduced in 4008704f62

The trailing comma is followed by `)` when the varargs list
is empty in the macro, which is a syntax error in C

This fixes compilation of code such as the following

    PHP_FUNCTION(get_metadata) {
      if (zend_parse_parameters_throw(ZEND_NUM_ARGS(), "") == FAILURE) {
        return;
      }

Closes GH-4896.