Map bright black (colour 8) to white (7) if the background is black on

terminals with only eight colours so the text is not invisible. From
Dmytro Bagrii in GitHub issue 4322.

tty.c

@@ -2758,6 +2758,8 @@ tty_check_fg(struct tty *tty, struct colour_palette *palette,
 				gc->fg &= 7;
 				if (colours >= 16)
 					gc->fg += 90;
+				else if (gc->fg == 0 && gc->bg == 0)
+					gc->fg = 7;
 			}
 		}
 		return;