try to fix unresolved external symbol error

and dividing by zero problem

Author: talregev

gtsam/geometry/Rot3.h

@@ -49,6 +49,9 @@
 
 namespace gtsam {
 
+template class GTSAM_EXPORT
+    OptionalJacobian<9, 3>;
+
 /**
  * @brief Rot3 is a 3D rotation represented as a rotation matrix if the
  * preprocessor symbol GTSAM_USE_QUATERNIONS is not defined, or as a quaternion

gtsam/linear/NoiseModel.h

@@ -575,6 +575,9 @@ namespace gtsam {
        * An isotropic noise model created by specifying a precision
        */
       static shared_ptr Precision(size_t dim, double precision, bool smart = true)  {
+        if (0 == precision) {
+          return nullptr;
+        }
         return Variance(dim, 1.0/precision, smart);
       }