Buffer size of 16 is not enough for the output, bump to 32
Specific bug can be triggered by adding >16 relays and using RelayMask
Since the used API does not check buffer size at all, it ended up
overwriting the stack just before the callsite. e.g. relay boot would
show relay count as 48 (aka '0')
Remove explicit reserve() as well, buffer concat will take care of that