Fix booting without CD in drive.

Index: qemu/hw/scsi-disk.c
===================================================================
--- qemu.orig/hw/scsi-disk.c	2006-08-13 19:44:42.000000000 +0000
+++ qemu/hw/scsi-disk.c	2006-08-13 19:49:58.000000000 +0000
@@ -109,8 +109,10 @@
     uint32_t n;

     DPRINTF("Read %d (%d/%d)\n", len, s->buf_len, s->sector_count);
-    if (s->buf_len == 0 && s->sector_count == 0)
+    if (s->buf_len == 0 && s->sector_count == 0) {
+        scsi_command_complete(s, SENSE_NO_SENSE);
         return 1;
+    }

     if (s->buf_len) {
         n = s->buf_len;
@@ -447,6 +449,7 @@
             s->buf_len = 8;
         } else {
             scsi_command_complete(s, SENSE_NOT_READY);
+            return 0;
         }
	break;
     case 0x08: