[PATCH] Fix PR libstdc++/19510: Uninitialized variable in some iterators

[Chris Jefferson]

>But copying singular iterators is explicitly disallowed, isn't it?
>
>24.1/5:
>   Iterators can also have singular values that are not associated with
>   any container. [Example: After the declaration of an uninitialized
>   pointer x (as with int* x;), x must always be assumed to have a
>   singular value of a pointer. ] Results of most expressions are
>   undefined for singular values; the only exception is an assignment of
>   a nonsingular value to an iterator that holds a singular value. In
>   this case the singular value is overwritten the same way as any other
>   value.
>
>This explicitly mentions the case of uninitialised pointers being
>singular.
>
>  
>
Just a quick note. 8.3.1/2, the line "pc = p", shows you can copy 
uninitalised pointers.

Chris