revisit display artifact appearing to the right of status line

The prior fix for this was a bit flawed. It was only considering
the length of the last field, but what it really needed to do was
consider the placement of the last character of the last field
on the row relative to the placement of the last character of
the last field on the row previously.

If the new placement of that last character of the last field
is left of the previous placement, some clearing must be done.

include/wintty.h

@@ -75,11 +75,11 @@ struct tty_status_fields {
     int color;
     int attr;
     int x, y;
+    int padright;
     size_t lth;
     boolean valid;
     boolean dirty;
     boolean redraw;
-    boolean padright;
 };
 #endif