Add T_freeze as an output for incompressibles

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>

src/AbstractState.cpp

@@ -199,6 +199,8 @@ double AbstractState::trivial_keyed_output(int key)
         return this->calc_fraction_min();
     case ifraction_max:
         return this->calc_fraction_max();
+    case iT_freeze:
+        return this->calc_T_freeze();
     default:
         throw ValueError(format("This input [%d: \"%s\"] is not valid for trivial_keyed_output",key,get_parameter_information(key,"short").c_str()));
     }