MDL-58948 behat: Fix spin method when callback throws exception

Was preventing the sleep statements from running.  This caused
steps to fail too early when it was just waiting for something
to change in the browser.

lib/behat/behat_base.php

@@ -335,8 +335,6 @@ protected function spin($lambda, $args = false, $timeout = false, $exception = f
                 if (!$exception) {
                     $exception = $e;
                 }
-                // We wait until no exception is thrown or timeout expires.
-                continue;
             }
 
             if ($this->running_javascript()) {