Allows disk flip autodetection in "The Big Demo" to work
(disk1 -> empty -> disk2 cycle and the opposite)
--- atari800-4.2.0/src/sio.c.orig	2019-12-28 18:00:29.000000000 +0100
+++ atari800-4.2.0/src/sio.c	2021-01-14 17:31:08.961358709 +0100
@@ -1083,7 +1083,9 @@
 		Log_print("Drive Status unit %d %x %x %x %x",unit,buffer[0], buffer[1], buffer[2], buffer[3]);
 		return 'C';
 	}	
-	buffer[0] = 16;         /* drive active */
+       /* DVSTAT0 bit 4: drive active(?)/motor on;
+          "The Big Demo" expects 0->1 trigger to detect disk insertion after "flip the disk" message */
+	buffer[0] = disk[unit] != NULL ? 16 : 0;
 	buffer[1] = disk[unit] != NULL ? 255 /* WD 177x OK */ : 127 /* no disk */;
 	if (io_success[unit] != 0)
 		buffer[0] |= 4;     /* failed RW-operation */