undefined index in line 913 of acquia_spi.module

preg_match('!^([^/]+)(/.+)?$!', $server['SERVER_SOFTWARE'], $webserver);
if (stristr($webserver[1], 'Apache') && function_exists('apache_get_version')) {

If $webserver does not have any match, it won't have index 1 and give a notice. Should be simple to fix