Resolve PHP 7.2 Errors

bootstrap.php

include/class.export.php

include/class.http.php

include/class.nav.php

include/class.orm.php

include/client/templates/thread-entries.tmpl.php

include/pear/Mail/mimePart.php

include/staff/profile.inc.php

include/staff/templates/queue-subnavigation.tmpl.php

include/staff/templates/thread-entries.tmpl.php