SmartRangeFactor warnings with gcc

[Chris Beall]

In file included from /home/cbeall3/git/gtsam/gtsam_unstable/slam/tests/testSmartRangeFactor.cpp:19:0:
/home/cbeall3/git/gtsam/gtsam_unstable/slam/SmartRangeFactor.h: In member function ‘gtsam::Point2 gtsam::SmartRangeFactor::triangulate(const gtsam::Values&) const’:
/home/cbeall3/git/gtsam/gtsam_unstable/slam/SmartRangeFactor.h:113:27: warning: ‘*((void*)(& best_fh)+8).gtsam::Point2::y_’ may be used uninitialized in this function [-Wmaybe-uninitialized]
       if (fh && (!best_fh || fh->y() > best_fh->y())) {
                           ^