Forward branches broken in AutoGrow mode

[zlateski]

To reproduce:

struct CodeWorks : Xbyak_aarch64::CodeGeneratorAArch64
{
    CodeWorks()
        : Xbyak_aarch64::CodeGeneratorAArch64(65536)
    {
        Xbyak::LabelAArch64 l;
        b(l);
        L_aarch64(l);
    }
};

struct CodeBroken : Xbyak_aarch64::CodeGeneratorAArch64
{
    CodeBroken()
        : Xbyak_aarch64::CodeGeneratorAArch64(65536, Xbyak_aarch64::AutoGrow)
    {
        Xbyak::LabelAArch64 l;
        b(l);
        L_aarch64(l);
    }
};

int main()
{
    {
        CodeWorks c;
        c.ready();
        std::cout << "Works" << std::endl;
    }
    {
        CodeBroken c;
        c.ready();
    }
}