sqsetcookie is called every time sqsession_is_active is called, which results in...

sqsetcookie is called every time sqsession_is_active is called, which results in headers-already-sent notices after output has been initiated... here is a fix

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@12872 7612ce4b-ef26-0410-bec9-ea0150e637f0