getTarget() returns empty unit on not found

Changed getTarget() in Unit.cpp to return Unit() if no target found

src/Unit.cpp

@@ -310,7 +310,7 @@ Unit Unit::getTarget() const
           return m_bot->GetUnit(t_id);
 	    }
 
-	return m_unit;
+	return Unit();
 }
 
 bool Unit::isBlip() const