Initialize pointers in POEMS

------------------------------------------------------------------------- */

FixPOEMS::FixPOEMS(LAMMPS *lmp, int narg, char **arg) :

  Fix(lmp, narg, arg)

  Fix(lmp, narg, arg), step_respa(NULL), natom2body(NULL), 

  atom2body(NULL), displace(NULL), nrigid(NULL), masstotal(NULL), 

  xcm(NULL), vcm(NULL), fcm(NULL), inertia(NULL), ex_space(NULL), 

  ey_space(NULL), ez_space(NULL), angmom(NULL), omega(NULL), 

  torque(NULL), sum(NULL), all(NULL), jointbody(NULL), 

  xjoint(NULL), freelist(NULL), poems(NULL)

{

  if (lmp->citeme) lmp->citeme->add(cite_fix_poems);