babl_fish_reference(), create_name() are racy

babl_fish_reference(), create_name() are racy

create_name_internal() uses global static buffer to create name.
While this is definitely fast, it can't work concurrently.

I used snprintf()+malloc()+snprintf(), so the amount of allocated
memory for the string is optimal.

Alternatively, a mutex would solve the problem, not sure which
solution is faster / better.