fixed gtk critical warning on undo action
fixed gtk critical warning on undo action

jmarshallnz/gummi,jmarshallnz/gummi,tonyolag/gummi-vim,tonyolag/gummi-vim,tonyolag/gummi-vim,tonyolag/gummi-vim,jmarshallnz/gummi,jmarshallnz/gummi