Correctly reset the splitting flag in space.c and cell.c

src/cell.c

@@ -316,6 +316,7 @@ int cell_unpack(struct pcell *restrict pc, struct cell *restrict c,
   int count = 1;
 
   /* Fill the progeny recursively, depth-first. */
+  c->split = 0;
   for (int k = 0; k < 8; k++)
     if (pc->progeny[k] >= 0) {
       struct cell *temp;

src/space.c

@@ -493,6 +493,7 @@ void space_regrid(struct space *s, int verbose) {
           c->width[2] = s->width[2];
           c->dmin = dmin;
           c->depth = 0;
+          c->split = 0;
           c->hydro.count = 0;
           c->grav.count = 0;
           c->stars.count = 0;