Correct SMSG_INSTANCE_DIFFICULTY structure (fixes raid difficulty display).

Move GetDifficulty() in under Map-scope, so it's reachable for map-based functions

--HG--
branch : trunk

src/game/Player.cpp

@@ -20713,6 +20713,10 @@ void Player::SendInitialPacketsBeforeAddToMap()
     SendTalentsInfoData(false);
 
     // SMSG_INSTANCE_DIFFICULTY
+    data.Initialize(SMSG_INSTANCE_DIFFICULTY, 4+4);
+    data << uint32(GetMap()->GetDifficulty());
+    data << uint32(0);
+    GetSession()->SendPacket(&data);
 
     SendInitialSpells();