added locking to dragon hoards

src/enemies/dragon.cc

@@ -1,10 +1,12 @@
 #include "dragon.h"
 
 #include "../constants.h"
+#include "../level.h"
 
 dragon::dragon(RNG *rng, const feature enabled_features, const position &pos,
-               const int gen_room_num):
-        enemy_base{rng, enabled_features, DRAGON, pos, gen_room_num, "D"} {}
+               const int gen_room_num, const position &guards):
+        enemy_base{rng, enabled_features, DRAGON, pos, gen_room_num, "D"},
+        guards{guards} {}
 
 const char *dragon::get_race_name() const {
         return "Dragon";
@@ -18,5 +20,9 @@ long_result dragon::act(level *lvl, character *pc, bool hostile) {
 }
 
 int dragon::dies(level *lvl) {
+        for (auto &g : lvl->get_glist())
+                if (g.get_pos() == guards)
+                        g.unlock();
+
         return 0;
 }