Bug with tab bar and event delivery to header line

[Cecilio Pardo]

Some mouse events are sent to the header line when the pointer is way 
below the header line. I think the problem may be the function 
coordinates_in_window. 
When testing for the header line, it uses the height of the tab bar:

 || (window_wants_header_line (w)
     && y < top_y + CURRENT_TAB_LINE_HEIGHT (w) 
                  + CURRENT_HEADER_LINE_HEIGHT (w)
         && (part = ON_HEADER_LINE)))

I checked that CURRENT_TAB_LINE_HEIGHT returns a big value even
when there is no tab bar. I don't know if that's correct or not.

-- 
Cecilio Pardo