[RFA] Fix crash when DW_AT_producer attribute is absent

[Joel Brobecker]

> > The crash happens because we do the following inside dwarf2read.c:
> > 
> >   attr = dwarf2_attr (die, DW_AT_producer, cu);
> >   if (attr)
> >     cu->producer = DW_STRING (attr);
> >   [...]
> >   record_producer (cu->producer);
> > 
> >   (but cu->producer is NULL)
> 
> OK and thanks.

Thanks Daniel. Checked in.

-- 
Joel