[Server] Fix Cell iterators

apps/openmw-mp/Cell.cpp

@@ -212,12 +212,12 @@ Cell::Cell(ESM::Cell cell): cell(cell)
 
 }
 
-Cell::Iterator Cell::begin()
+Cell::Iterator Cell::begin() const
 {
     return players.begin();
 }
 
-Cell::Iterator Cell::end()
+Cell::Iterator Cell::end() const
 {
     return players.end();
 }

apps/openmw-mp/Cell.hpp

@@ -53,10 +53,10 @@ class Cell
 public:
     Cell(ESM::Cell cell);
     typedef std::deque<Player*> TPlayers;
-    typedef TPlayers::iterator Iterator;
-    
-    Iterator begin();
-    Iterator end();
+    typedef TPlayers::const_iterator Iterator;
+
+    Iterator begin() const;
+    Iterator end() const;
 
     void addPlayer(Player *player);
     void removePlayer(Player *player);