Buffer overflow in toml_string_in_overwrite

[AKuHAK]

When using various toml files (like system and later user-defined) the data may become corrupted:
example in system toml
default_bsdfs=hdl
in user toml
default_bsdfs=exfat

then it will result in
sys.sBSDFS: exD

[rickgaiser]

I've never seen this before. I will test this when I get the chance.

[rickgaiser]

I was not able to reproduce, but also not happy with the current TOML string handling. I changes them all to properly malloc/free a new buffer for each string used.

Can you try again and see if it's fixed?