[ci optional] Made ideal xnefer 1d-20 to prevent overflow.

Author: adamjermyn

eos/private/ideal.f90

@@ -126,7 +126,7 @@ subroutine ideal_eos( &
 
       ! No electrons, so extreme negative chemical potential
       etaele = -1d99
-      xnefer = 1d-99
+      xnefer = 1d-20
 
       ! no latent heat
       latent_ddlnT = 0d0