Show e-mail checkbox is always enabled

[navjottomer]

In the new version of the site, the Show e-mail checkbox is always enabled, it cannot be turned off even by the administrator.

Originally posted by @buninsan in https://github.com/mindstellar/Osclass/discussions/435#discussioncomment-1659984

[eurobank]

@buninsan Does this fix work for you?

[patriksh]

This fixed the "always enabled" but there's still problems with how value is read from session. For me it now always kept it unchecked.

if (Session::newInstance()->_getForm('showEmail') != 0) should probably be if (Session::newInstance()->_getForm('showEmail') != "") in show_email_checkbox.