Free data on RawData.resize(0)

[marcgurevitx]

In the previous RawData patch I've introduced UB by realloc to size 0. On my Linux it core-dumped on this:

> r = new RawData
> r.resize 0
> r.resize 0
> r.resize 0
free(): double free detected in tcache 2
Aborted (core dumped)

This PR should fix it.