Optimisation of one loop when computing solar radiation (with SOLRAD)

When solar radiation (RAY3) is not read in the atmospheric data file by WAQTEL, the call to SOLRAD is done for every 2D node and every plane in CALCS3D_THERMICV and CALCS3D_AED2 whereas it is only dependent on 2D node. The loop can be optimised a little bit.