code improvements for the viewer

[Roland Illig]

Pavel Tsekov wrote:
> Ok, here we go. I saw this coming but anyway. And no I don't like to blame
> you.
> 
> Quick View mode isn't working anymore. It is even funnier because the
> behaviour differs between slang and ncurses. You deserve to be blamed
> because you haven't tested the Quick View mode at all.

The "at all" is not correct. Indeed, I have left out the case where 
mcview is shown in the right panel. I have fixed it. Thanks for testing 
and the quick note.

> Now the details.
> 
> 1) MC with slang
> 
>    If I change to Quick View mode the panel holding the quick view (right
>    panel in this case) doesn't display any text and the header line.
> 
> 2) MC with ncurses
> 
>    Text is displayed, but IMO it doesn't fit well in the viewer area. It
>    even is drawn in the space that should be occupied by the border.
>    Header line is displayed but at the end of the text not at the start.
>    The header line doesn't always have contents - i.e. if the file is not
>    empty the header line contains what it is supposed to contain but in
>    other cases it doesn't

These two bugs are essentially the same. When trying to write something 
outside the defined screen area, SLang just discards it while ncurses 
writes it into the next line, scrolling down if necessary.

My fault was that I did not compute the areas for the status line, ruler 
  and data relative to the widget, but relative to the parent dialog. I 
didn't notice the bug because I only switched the left panel into 
quick-view mode and because I have the menu bar hidden.

Roland