Fix https://github.com/unicorn-engine/unicorn/issues/1586

[liyansong2018]

If uc->init_arch == NULL, uc need to be retruned because it already points to heap space. Of course, we can also directly free the corresponding memory space.

if (uc->init_arch == NULL) {
    free(uc);
    return UC_ERR_ARCH;
}

[wtdcode]

Merged, thanks.