winpr: fixed incorrect pipe reference count usage

- refcount is only relevant for servermode
- refcount was used uninitialized in clientmode
- credit for fix goes to @bmiklautz

Bug was introduced by 5e09e37d42bd8896a687df830a95f5cb56e4d47c
Merge pull request #1866 from nfedera/fix-2014-05-26-01

winpr: fixed incorrect pipe reference count usage