Ticket #3179: do not consider "String not found" mwssage as error.

If some string isn't found it is a normal situation, not en error.
So show "String not found" message as normal dialog not as error one.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Merge branch '3179_not_found_dialog_uniq'

* 3179_not_found_dialog_uniq:
  Ticket #3179: do not consider "String not found" mwssage as error.