RFR (S) 8217994: os::print_hex_dump should be more resilient against unreadable memory

[Aleksey Shipilev]

On 1/30/19 11:48 AM, Schmidt, Lutz wrote:
> When looking at the newly introduced else branch, I had the idea of replacing the entire switch by
> 
>   st->print("%*s", 2*unitsize, "????????????????");
> 
> Like it? I do!

That's a cute trick, but I don't think it works: the format width is the _minimal_ width, and the
that 16-wide string argument would not be truncated to 2*unitsize.

-Aleksey