Draw component port as filled square when it has only one connection

[wawuwo]

This is a fix of regression introduced in 4e9e968.

When I was adapting the Node::paint to QPainter I made a mistake in translation from couple of braceless ifs to if blocks with braces. Compare this:

    case 2:  if(Connections.getFirst()->Type == isWire)
               if(Connections.getLast()->Type == isWire) return;
             p->fillRect(cx-2, cy-2, 4, 4, Qt::darkBlue);
             break;

and this

    case 2:
      if (Connections.getFirst()->Type == isWire) {
        if (Connections.getLast()->Type == isWire) {
          painter->restore();
          return;
        }
        painter->fillRect(cx-2, cy-2, 4, 4, Qt::darkBlue);
      }
      break;

— the former is logical AND of two conditions, and the latter is something else.

The problem with component port rendering is described in #818