BUG: cellCuts: incorrect correspondence. Fixes #670.

src/dynamicMesh/meshCut/cellCuts/cellCuts.C

@@ -242,7 +242,12 @@ void Foam::cellCuts::syncProc()
                             else
                             {
                                 label oppFp = relCut[i]-1;
-                                label fp = f.size()-1-oppFp;
+                                label fp =
+                                (
+                                    oppFp == 0
+                                  ? 0
+                                  : f.size()-oppFp
+                                );
                                 absoluteCut[i] = vertToEVert(f[fp]);
                             }
                         }