Fix Session cookie driver storing untrimmed user agent string in the database causing set_userdata() calls to fail when $config['sess_match_useragent'] = TRUE

Signed-off-by: Daniel Robbins <github@danieljrobbins.com>
diff --git a/system/libraries/Session/drivers/Session_cookie.php b/system/libraries/Session/drivers/Session_cookie.php
index 057e5a1..0e86441 100644
--- a/system/libraries/Session/drivers/Session_cookie.php
+++ b/system/libraries/Session/drivers/Session_cookie.php
@@ -494,7 +494,7 @@
 		$this->userdata = array(
 			'session_id'	=> $this->_make_sess_id(),
 			'ip_address'	=> $this->CI->input->ip_address(),
-			'user_agent'	=> substr($this->CI->input->user_agent(), 0, 120),
+			'user_agent'	=> trim(substr($this->CI->input->user_agent(), 0, 120)),
 			'last_activity'	=> $this->now,
 		);