functionObjects::forceCoeffs: Corrected setting of rhoRef for compressible flow

Resolves bug-report https://bugs.openfoam.org/view.php?id=2387

src/functionObjects/forces/forceCoeffs/forceCoeffs.C

@@ -163,6 +163,9 @@ bool Foam::functionObjects::forceCoeffs::read(const dictionary& dict)
     // Free stream velocity magnitude
     dict.lookup("magUInf") >> magUInf_;
 
+    // Reference (free stream) density
+    dict.lookup("rhoInf") >> rhoRef_;
+
     // Reference length and area scales
     dict.lookup("lRef") >> lRef_;
     dict.lookup("Aref") >> Aref_;

src/functionObjects/forces/forces/forces.C

@@ -638,7 +638,7 @@ bool Foam::functionObjects::forces::read(const dictionary& dict)
         // Reference density needed for incompressible calculations
         if (rhoName_ == "rhoInf")
         {
-            rhoRef_ = readScalar(dict.lookup("rhoInf"));
+            dict.lookup("rhoInf") >> rhoRef_;
         }
 
         // Reference pressure, 0 by default