Show unicode box drawing characters with bitmap fonts

[Qrox]

Summary

SUMMARY: Bugfixes "Fix roads not drawn in the overmap when using bitmap font without SDL line drawing"

Purpose of change

The symbols for overmap road tiles are unicode box drawing characters, so if SDL line drawing is disabled, and bitmap font is used (such as when using the Graphical Overmap mod), roads will not be correctly drawn.

Describe the solution

Check if the character being drawn is a unicode box drawing character in BitmapFont::OutputChar, and use BitmapFont::draw_ascii_lines in such case.

Describe alternatives you've considered

I considered converting the bitmap font of Graphical Overmap to a ttf font, but that would probably be harder to maintain if someone wants to add more characters to the font in the future.

Testing

Roads in the overmap are now correctly drawn with this change.