hw/display/artist: Fix draw_line() artefacts

The draw_line() function left artefacts on the screen because it was using the
x/y variables which were incremented in the loop before. Fix it by using the
unmodified x1/x2 variables instead.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: qemu-stable@nongnu.org
Signed-off-by: Helge Deller <deller@gmx.de>

hw/display/artist.c

@@ -553,10 +553,11 @@ static void draw_line(ARTISTState *s,
         }
         x++;
     } while (x <= x2 && (max_pix == -1 || --max_pix > 0));
+
     if (c1)
-        artist_invalidate_lines(buf, x, dy+1);
+        artist_invalidate_lines(buf, x1, x2 - x1);
     else
-        artist_invalidate_lines(buf, y, dx+1);
+        artist_invalidate_lines(buf, y1 > y2 ? y2 : y1, x2 - x1);
 }
 
 static void draw_line_pattern_start(ARTISTState *s)