Surface: Don't draw_char() if x < 0 or y < 0.
Surface: Don't draw_char() if x < 0 or y < 0.

This should prevent unnecessarily drawing sprites which are off the top or the
left of the surface.

Signed-off-by: aszlig <ee1aa092358634f9c53f01b5a783726c9e21b35a@redmoonstudios.org>

aszlig/hase