REF_AREA=0 causes immediate divergence when totalpositivearea=0

[bigfooted]

Describe the bug
From cfd-online:
https://www.cfd-online.com/Forums/su2/259230-nan-error-before-iterations-begin-3d-su2.html#post879476
"I found the problem. The setting of REF_AREA = 0, which worked in the Turbulent ONERA M6 tutorial and I understand is supposed to imply an automatic calculation, in this case caused the error. "

REF_AREA=0 triggers a recomputation of the area, in CPhysicalGeometry::SetPositive_ZArea :

 if (config->GetRefArea() == 0.0) {
    if (D3)
      config->SetRefArea(TotalPositiveZArea);
    else
      config->SetRefArea(TotalPositiveYArea);

This does not work if the totalpositivearea is zero (I think this is the reason of immediate divergence in this case). We should warn the user that this is the case, and stop with an error message

[vkrm1612]

Hi, I have corrected the bug as mentioned, can you please give me those example mesh and cfg files so that I can use it to verify them, when I am trying use the existing files from cfd forum I am getting errors.

[pcarruscag]

What errors do you get?