Only check 2nd order multipole terms if they exist

src/cell.c

@@ -827,6 +827,7 @@ void cell_check_multipole(struct cell *c, void *data) {
         error("Multipole CoM are different (%12.15e vs. %12.15e", ma.CoM[k],
               mb.CoM[k]);
 
+#if const_gravity_multipole_order >= 2
     if (fabsf(ma.I_xx - mb.I_xx) / fabsf(ma.I_xx + mb.I_xx) > 1e-5 &&
         ma.I_xx > 1e-9)
       error("Multipole I_xx are different (%12.15e vs. %12.15e)", ma.I_xx,
@@ -851,6 +852,7 @@ void cell_check_multipole(struct cell *c, void *data) {
         ma.I_yz > 1e-9)
       error("Multipole I_yz are different (%12.15e vs. %12.15e)", ma.I_yz,
             mb.I_yz);
+#endif
   }
 }