[RFA] print error message if (auto) disassembly failed

[Joel Brobecker]

> >     (gdb) core core
> >     warning: core file may not match specified executable file.
> >     Core was generated by `./crash'.
> >     Program terminated with signal 6, Aborted.
> >     #0  0x00007fe6fe543307 in ?? ()
> >     0x00007fe6fe543307:     (cannot read memory)
> 
> Fine with me, although "cannot read memory" is a bit more general,
> English-wise, than the actual cause, which is that this specific
> address is unreadable.

I did not line "address unreadable" because we weren't reading
an address, we were reading the memory at that address, shown
on the left hand side.  That's why I proposed this instead, which
in my opinion is more accurate.

-- 
Joel