xmllite: Avoid warning in test_read_state related to -1 not being in XmlReadState.

[Gerald Pfeifer]

On Sat, 4 Nov 2017, Nikolay Sivov wrote:
> Is this warning enabled by default in some release clang version? I'm 
> not necessarily opposed in silencing it like that, but I imagine you'll 
> see many more instances like that, and if it's not default set of 
> warnings I don't know if we should bother.

Yes, this happens with completely default clang as it is the
system compiler on FreeBSD 10, reporting itself as clang 3.4.1.

Otherwise I would probably side with "let's not bother" as well 
(and usually use GCC to build Wine).

Gerald