Core: Clean up here and there.

*replase postfix iterator increment\decrement with prefix in cycles
*replase strlen(*char) != 0 with *char[0] != '\0'
*replase strlen(rStr.c_str()) with rStr.length()

src/server/game/Battlegrounds/Battleground.cpp

@@ -1664,7 +1664,7 @@ void Battleground::SendWarningToAll(int32 entry, ...)
     data << (uint32)1;
     data << (uint8)0;
     data << (uint64)0;
-    data << (uint32)(strlen(msg.c_str())+1);
+    data << (uint32)(msg.length() + 1);
     data << msg.c_str();
     data << (uint8)0;
     for (BattlegroundPlayerMap::const_iterator itr = m_Players.begin(); itr != m_Players.end(); ++itr)