[Qt] simplify return code and return values in txtablemodel
[Qt] simplify return code and return values in txtablemodel

- also move an added space in a string where it belongs

(cherry picked from commit bbad683224c77743a9fef5cc2fc64cc43fbec192)

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin