polyMesh: Ensure parallel consistency in findCell

by ensuring tetBasePtIs is called on all processors, even for those with
0 cells.  Also use unique communicator for globalMeshData to avoid data
transfer interference.

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1792

src/OpenFOAM/meshes/polyMesh/globalMeshData/globalMeshData.C

@@ -2748,7 +2748,12 @@ void Foam::globalMeshData::updateMesh()
 
     // *** Temporary hack to avoid problems with overlapping communication
     // *** between these reductions and the calculation of deltaCoeffs
-    label comm = UPstream::worldComm + 1;
+    label comm = UPstream::allocateCommunicator
+    (
+        UPstream::worldComm,
+        identity(UPstream::nProcs()),
+        true
+    );
 
     // Total number of faces.
     nTotalFaces_ = returnReduce
@@ -2785,6 +2790,8 @@ void Foam::globalMeshData::updateMesh()
         comm
     );
 
+    UPstream::freeCommunicator(comm);
+
     if (debug)
     {
         Pout<< "globalMeshData : nTotalPoints_:" << nTotalPoints_ << endl;

src/OpenFOAM/meshes/polyMesh/polyMesh.C

@@ -1478,12 +1478,11 @@ Foam::label Foam::polyMesh::findCell
     const cellDecomposition decompMode
 ) const
 {
-    if (nCells() == 0)
-    {
-        return -1;
-    }
-
-    if (Pstream::parRun() && decompMode == FACE_DIAG_TRIS)
+    if
+    (
+        Pstream::parRun()
+     && (decompMode == FACE_DIAG_TRIS || decompMode == CELL_TETS)
+    )
     {
         // Force construction of face-diagonal decomposition before testing
         // for zero cells.
@@ -1494,6 +1493,11 @@ Foam::label Foam::polyMesh::findCell
         (void)tetBasePtIs();
     }
 
+    if (nCells() == 0)
+    {
+        return -1;
+    }
+
     if (decompMode == CELL_TETS)
     {
         // Advanced search method utilizing an octree