[perl #113988] [BUG] Null PMC access when doing .fmt on the return value from .reals

[Carl Mäsak via RT]

coke:
> Lists's .fmt is using the full format on each value in the list, so
> you get the same effect with:
> 
> > 3.fmt("%d %d");
> Null PMC access in get_integer()

So it's a dupe of <https://rt.perl.org/rt3/Ticket/Display.html?
id=106594>, really. I could merge them; any objections?