Make ‘No such class’ apply to ${$ref}{key}, too

Make ‘No such class’ apply to ${$ref}{key}, too

$ perl -le 'use fields "foo"; my main $r; $r->{bar}'
No such class field "bar" in variable $r of type main at -e line 1.
$ perl -le 'use fields "foo"; my main $r; $$r{bar}'
No such class field "bar" in variable $r of type main at -e line 1.
$ perl -le 'use fields "foo"; my main $r; ${$r}{bar}'
$

Notice how the last one is silent.  There is already code to handle
the block for hash slices, so we can copy that.