reactingParcelFoam and chtMultiRegionFoam: Always solve the density equation

A clause preventing solution of the density equation has been removed
from reactingParcelFoam and chtMultiRegionFoam, so that they are nore
consistent with other compressible solvers. In general, the density
equation is solved before the pimple loop is entered to make sure that
the flux and the density derivative are consistent during the first
pimple iteration.

applications/solvers/heatTransfer/chtMultiRegionFoam/fluid/solveFluid.H

@@ -4,7 +4,7 @@ if (pimple.frozenFlow())
 }
 else
 {
-    if (!mesh.steady() && pimples.nCorrPimple() <= 1)
+    if (!mesh.steady() && pimples.firstPimpleIter())
     {
         #include "rhoEqn.H"
     }

applications/solvers/lagrangian/reactingParcelFoam/reactingParcelFoam.C

@@ -93,11 +93,8 @@ int main(int argc, char *argv[])
         surfaceFilm.evolve();
 
         if (solvePrimaryRegion)
-        {
-            if (pimple.nCorrPimple() <= 1)
         {
             #include "rhoEqn.H"
-            }
 
             // --- PIMPLE loop
             while (pimple.loop())