Bus may report all-ones when trying to access non-existent extended space.
Same check is also in lib/caps.c extended space parser.
if (!config_fetch(d, where, 4))
break;
header = get_conf_long(d, where);
if (!config_fetch(d, where, 4))
break;
header = get_conf_long(d, where);
+ if (!header || header == 0xffffffff)
break;
id = header & 0xffff;
version = (header >> 16) & 0xf;
break;
id = header & 0xffff;
version = (header >> 16) & 0xf;