render-cg: fix potential VRAM overflow in gint_dhline()

A missing coordinate check in gint_dhline() would allow lines entirely
out of bounds of the screen to write pixels outside of their expected
range, often wrapping up to the next line, but possibly overflowing from
VRAM.

src/render-cg/dline.c

@@ -7,6 +7,7 @@ void gint_dhline(int x1, int x2, int y, uint16_t color)
 	/* Order and bounds */
 	if((uint)y >= 224) return;
 	if(x1 > x2) swap(x1, x2);
+	if(x1 >= 396 || x2 < 0) return;
 	if(x1 < 0) x1 = 0;
 	if(x2 >= 396) x2 = 395;