Don't divide by time-step if time-step is zero in the hydro_kick

src/hydro/Gadget2/hydro.h

@@ -377,7 +377,7 @@ __attribute__((always_inline)) INLINE static void hydro_kick_extra(
     struct part *restrict p, struct xpart *restrict xp, float dt) {
 
   /* Do not decrease the entropy by more than a factor of 2 */
-  if (p->entropy_dt < -0.5f * xp->entropy_full / dt) {
+  if (dt > 0. && p->entropy_dt * dt < -0.5f * xp->entropy_full) {
     /* message("Warning! Limiting entropy_dt. Possible cooling error.\n
      * entropy_full = %g \n entropy_dt * dt =%g \n", */
     /* 	     xp->entropy_full,p->entropy_dt * dt); */