Wrap warning

[Frank Dellaert]

[  6%] Building CXX object wrap/CMakeFiles/wrap_lib.dir/Module.cpp.o
/Users/frank/borg/gtsam/wrap/Module.cpp:330:86: warning: variable 'namespace_def_p' is
      uninitialized when used within its own initialization [-Wuninitialized]
  ...class_p | templateSingleInstantiation_p | global_function_p | namespace_def_p | com...
                                                                   ^~~~~~~~~~~~~~~

[Richard Roberts]

Fixed.