XGA: Cursor no longer gets black parts when returning from Mystify screensaver to GUI and, at the same time, keeping the Win95 cursor intact.

Mono blits no longer cause transparency issues in some programs (e.g.: Creative utilities such as MIDI and CD on Win3.1x).

src/include/86box/vid_xga.h

@@ -92,7 +92,7 @@ typedef struct xga_t {
     int on;
     int op_mode_reset, linear_endian_reverse;
     int sprite_pos, sprite_pos_prefetch, cursor_data_on;
-    int pal_test;
+    int pal_test, a5_test;
     int type, bus;
 
     uint32_t linear_base, linear_size, banked_mask;