Do not recurse in runner_do_timestep() if the cell is inactive. Just reset the counters to zero.

src/runner.c

@@ -1135,6 +1135,14 @@ void runner_do_timestep(struct runner *r, struct cell *c, int timer) {
 
   TIMER_TIC;
 
+  /* Anything to do here? */
+  if (!cell_is_active(c, e)) {
+    c->updated = 0;
+    c->g_updated = 0;
+    c->s_updated = 0;
+    return;
+  }
+
   int updated = 0, g_updated = 0, s_updated = 0;
   integertime_t ti_end_min = max_nr_timesteps, ti_end_max = 0, ti_beg_max = 0;