fixing the initialization of aquifer pressure for CT aquifer

opm/simulators/aquifers/AquiferCarterTracy.hpp

@@ -266,7 +266,8 @@ protected:
         }
 
         // We take the average of the calculated equilibrium pressures.
-        Scalar aquifer_pres_avg = std::accumulate(pw_aquifer.begin(), pw_aquifer.end(), 0.) / pw_aquifer.size();
+        const Scalar sum_alpha = std::accumulate(this->alphai_.begin(), this->alphai_.end(), 0.);
+        const Scalar aquifer_pres_avg = std::accumulate(pw_aquifer.begin(), pw_aquifer.end(), 0.) / sum_alpha;
         return aquifer_pres_avg;
     }
 }; // class AquiferCarterTracy