Fix initial capacity of emitter

[Krotki]

When you use tb_out_reserve right away after emitter creation with byte count > 64, it will allocate only 64 bytes and set capacity of to 64.

In elf64.c file we see:

    TB_Emitter strtbl = { 0 };
    tb_out_reserve(&strtbl, 1024); // strtbl will have 64 capacity
    tb_out1b(&strtbl, 0);

with latter usage of tb_out_*_UNSAFE results in overwrite of random memory ...