Correct T_pSX in moist air to avoid simulation error when size X is 1

[CorentinLepais]

The current implementation of the function T_psX in Moist Air leads to a simulation error when using the function without providing the complete mass fraction X vector {X[Water],X[Air]}. The function has been updated to test the size of the input mass fraction vector X and re-calculate the mass fraction of air X[Air] if missing.

Closes #302

[CorentinLepais]

Regression tests ok

[RaphaelGebhart]

@CorentinLepais Works perfect for me. Would you suggest to create also a pull request for the MSL?

Attached my test example, which could easily be adapted to the MSL.
MoistAirEntropy.txt

[CorentinLepais]

I already created an issue in the MSL:Simulation error when using MoistAir.T_psX and described the problem and the solution but I did not create a pull request neither added a test example so if you want you can just update the issue with it

[RaphaelGebhart]

I already created an issue in the MSL:Simulation error when using MoistAir.T_psX and described the problem and the solution but I did not create a pull request neither added a test example so if you want you can just update the issue with it

Ok i created a pull request :)
modelica/ModelicaStandardLibrary#4781