eliminate some possible null-pointer exceptions

src/battle.c

@@ -218,6 +218,7 @@ static void message_faction(battle * b, faction * f, struct message *m)
     assert(f);
     if (f->battles == NULL || f->battles->r != r) {
         struct bmsg *bm = (struct bmsg *)calloc(1, sizeof(struct bmsg));
+        assert(bm || !"out of memory");
         bm->next = f->battles;
         f->battles = bm;
         bm->r = r;
@@ -251,6 +252,7 @@ static void fbattlerecord(battle * b, faction * f, const char *s)
 static bool set_enemy(side * as, side * ds, bool attacking)
 {
     int i;
+    assert(as && ds);
     for (i = 0; i != MAXSIDES; ++i) {
         if (ds->enemies[i] == NULL)
             ds->enemies[i] = as;
@@ -1942,12 +1944,14 @@ int skilldiff(troop at, troop dt, int dist)
                 is_protected = 2;
             }
         }
+        if (df->building->type->protection) {
             if (magicwalls_ct
                 && curse_active(get_curse(df->building->attribs, magicwalls_ct))) {
                 /* Verdoppelt Burgenbonus */
                 skdiff -= df->building->type->protection(df->building, du, DEFENSE_BONUS);
             }
         }
+    }
     /* Goblin-Verteidigung
      * ist direkt in der Rassentabelle als df_default
      */

src/move.c

@@ -127,6 +127,7 @@ get_followers(unit * target, region * r, const region_list * route_end,
             const attrib *a = a_find(uf->attribs, &at_follow);
             if (a && a->data.v == target) {
                 follower *fnew = (follower *)malloc(sizeof(follower));
+                assert(fnew || !"out of memory");
                 fnew->uf = uf;
                 fnew->ut = target;
                 fnew->route_end = route_end;
@@ -585,19 +586,22 @@ static void leave_trail(ship * sh, region * from, region_list * route)
 
             while (a != NULL && a->type == &at_shiptrail) {
                 td = (traveldir *)a->data.v;
-                if (td->no == sh->no)
+                if (td->no == sh->no) {
+                    td->dir = dir;
+                    td->age = 2;
                     break;
+                }
                 a = a->next;
             }
 
-            if (a == NULL || a->type != &at_shiptrail) {
+            if (a == NULL) {
                 a = a_add(&(r->attribs), a_new(&at_shiptrail));
                 td = (traveldir *)a->data.v;
                 td->no = sh->no;
-            }
                 td->dir = dir;
                 td->age = 2;
             }
+        }
         route = route->next;
         r = rn;
     }
@@ -769,8 +773,9 @@ static void msg_to_ship_inmates(ship *sh, unit **firstu, unit **lastu, message *
             *lastu = u->next;
         }
     }
-    if (shipfirst)
+    if (shipfirst) {
         *firstu = shipfirst;
+    }
     for (u = *firstu; u != *lastu; u = u->next) {
         freset(u->faction, FFL_MARK);
     }
@@ -1540,6 +1545,7 @@ static arg_regions *var_copy_regions(const region_list * begin, int size)
         assert(size > 0);
         arg_regions *dst =
             (arg_regions *)malloc(sizeof(arg_regions) + sizeof(region *) * (size_t)size);
+        assert(dst || !"out of memory");
         dst->nregions = size;
         dst->regions = (region **)(dst + 1);
         for (rsrc = begin; i != size; rsrc = rsrc->next) {

src/spells.c

@@ -1263,6 +1263,7 @@ add_ironweapon(const struct item_type *type, const struct item_type *rusty,
 float chance)
 {
     iron_weapon *iweapon = malloc(sizeof(iron_weapon));
+    assert(iweapon || !"out of memory");
     iweapon->type = type;
     iweapon->rusty = rusty;
     iweapon->chance = chance;