Fix use of libvorbisidec if libvorbisfile doesn't exist

[robho]

This is the problem:

dlopen(); // fails dlopen(); // succeeds dlerror(); // returns the error from the first dlopen()

[ralph-irving]

Thanks for the PR. Please don't move variables into associated block. Doing so, breaks squeezelite builds for older platform compilers. Could you move the err pointer back to it's original location?

[robho]

I moved the declaration back.

(I think it should be enough to keep variable declarations at the beginning of a scope (at least for c89 compliance), but I don't know all exotic compilers :-) Anyway, it makes sense to be consistent..)

[ralph-irving]

Thanks for moving the declaration back, I've merged your changes. The 32bit windows binaries are still compiled with VS2008.