Ticket #2706: hex viewer: continue search doesn't work.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Don't adjust viewer parameters twice after search in the hex mode.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Search callbacks should return mc_search_cbret_t not int.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>