[GSPH] EOS ignored beyond the uint field check

[tdavidcl]

https://github.com/tdavidcl/Shamrock/blame/0fe76c0585617b9932e584eb5702533f6a73cce9/src/shammodels/gsph/src/Solver.cpp#L1257-L1291

Here either we have an EOS with adiabatic and it works if the EOS has no uint field then it fallbacks silently to isothermal cs=1 regardless of the rest