Added minimal internal energy limit to kick_extra for PU scheme

src/hydro/PressureEnergy/hydro.h

@@ -593,6 +593,14 @@ __attribute__((always_inline)) INLINE static void hydro_kick_extra(
   }
   xp->u_full += p->u_dt * dt_therm;
 
+  /* Apply the minimal energy limit */
+  const float min_energy =
+      hydro_props->minimal_internal_energy / cosmo->a_factor_internal_energy;
+  if (xp->u_full < min_energy) {
+    xp->u_full = min_energy;
+    p->u_dt = 0.f;
+  }
+
   /* Compute the sound speed */
   const float soundspeed = hydro_get_comoving_soundspeed(p);