atapi: Drives can be locked without media present

Drivers are free to lock drives without any media present.  Such a
condition should not result in an error condition.

See Table 341 in MMC-5 spec for details.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

hw/ide/core.c

@@ -1230,13 +1230,8 @@ static void ide_atapi_cmd(IDEState *s)
         ide_atapi_cmd_reply(s, 18, max_len);
         break;
     case GPCMD_PREVENT_ALLOW_MEDIUM_REMOVAL:
-        if (bdrv_is_inserted(s->bs)) {
-            bdrv_set_locked(s->bs, packet[4] & 1);
-            ide_atapi_cmd_ok(s);
-        } else {
-            ide_atapi_cmd_error(s, SENSE_NOT_READY,
-                                ASC_MEDIUM_NOT_PRESENT);
-        }
+        bdrv_set_locked(s->bs, packet[4] & 1);
+        ide_atapi_cmd_ok(s);
         break;
     case GPCMD_READ_10:
     case GPCMD_READ_12: