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/Combat/ThreatManager.cpp

@@ -301,7 +301,7 @@ HostileReference* ThreatContainer::selectNextVictim(Creature* attacker, HostileR
     bool noPriorityTargetFound = false;
 
     std::list<HostileReference*>::const_iterator lastRef = iThreatList.end();
-    lastRef--;
+    --lastRef;
 
     for (std::list<HostileReference*>::const_iterator iter = iThreatList.begin(); iter != iThreatList.end() && !found;)
     {