bug#21173: 25.0.50; New frames positioned off screen with multiple monitors

[martin rudalics]

> Function x_calc_absolute_position does not account for the fact
> that my left monitor's left offsets are negative.  I believe that
> is the root of the bug.

If `display-monitor-attributes-list' returns the correct geometry values
it shouldn't be too hard to fix this.  That is, after the final
calculation of f->left_pos in x_calc_absolute_position subtract from it
the value (if negative) of whatever w32_display_monitor_attributes_list
returns as first value in `geometry' and from f->top_pos the second
value.  I can't test this here so it makes little sense to code it.

If you see the problem elsewhere too, we should probably postpone the
adjustment sketched above to my_set_window_pos in w32term.c.

martin