This fixes a bug where scroll lock would not work for tty #0 when using
vt_vga's textmode. The reason was that this window is created with a
static 256x100 buffer, larger than the real size of 80x25.
Now, in vt_change_font() and vt_compute_drawable_area(), we still
perform operations even of the window has no font loaded (this is the
case in textmode here vw->vw_font == NULL). One of these operation
resizes the buffer accordingly.
In vt_compute_drawable_area(), we take the terminal size as is (ie.
80x25) for the drawable area.
The font argument to vt_set_border() is removed (it was never used) and
the code now uses the computed drawable area instead of re-doing its own
calculation.
Reported by: Harald Schmalzbauer <h.schmalzbauer_omnilan.de>
Tested by: Harald Schmalzbauer <h.schmalzbauer_omnilan.de>
MFC after: 3 days
313ef9368f