Always initialise the gparts to a sensible state

src/cell.c

@@ -605,6 +605,26 @@ void cell_init_parts(struct cell *c, void *data) {
   c->ti_end_max = 0;
 }
 
+/**
+ * @brief Initialises all g-particles to a valid state even if the ICs were
+ *stupid
+ *
+ * @param c Cell to act upon
+ * @param data Unused parameter
+ */
+void cell_init_gparts(struct cell *c, void *data) {
+
+  struct gpart *gp = c->gparts;
+  const int gcount = c->gcount;
+
+  for (int i = 0; i < gcount; ++i) {
+    gp[i].ti_begin = 0;
+    gp[i].ti_end = 0;
+  }
+  c->ti_end_min = 0;
+  c->ti_end_max = 0;
+}
+
 /**
  * @brief Converts hydro quantities to a valid state after the initial density
  *calculation

src/cell.h

@@ -178,6 +178,7 @@ int cell_getsize(struct cell *c);
 int cell_link_parts(struct cell *c, struct part *parts);
 int cell_link_gparts(struct cell *c, struct gpart *gparts);
 void cell_init_parts(struct cell *c, void *data);
+void cell_init_gparts(struct cell *c, void *data);
 void cell_convert_hydro(struct cell *c, void *data);
 void cell_clean_links(struct cell *c, void *data);
 

src/engine.c

@@ -1846,7 +1846,15 @@ void engine_init_particles(struct engine *e) {
 
   /* Make sure all particles are ready to go */
   /* i.e. clean-up any stupid state in the ICs */
-  space_map_cells_pre(s, 1, cell_init_parts, NULL);
+  if ((e->policy & engine_policy_hydro) == engine_policy_hydro) {
+    space_map_cells_pre(s, 1, cell_init_parts, NULL);
+  }
+  if (((e->policy & engine_policy_self_gravity) ==
+       engine_policy_self_gravity) ||
+      ((e->policy & engine_policy_external_gravity) ==
+       engine_policy_external_gravity)) {
+    space_map_cells_pre(s, 1, cell_init_gparts, NULL);
+  }
 
   engine_prepare(e);