BUG: distanceSurface has gaps in mesh (#1374)

- need to be more generous when prefiltering the cell selection

src/sampling/surface/distanceSurface/distanceSurface.C

@@ -207,6 +207,9 @@ void Foam::distanceSurface::createGeometry()
                     cellBb.clear();
                     cellBb.add(fvm.points(), fvm.cellPoints(i));
 
+                    // Expand slightly to catch corners
+                    cellBb.inflate(0.1);
+
                     if (!cellBb.contains(nearest[i].hitPoint()))
                     {
                         ignoreCells.set(i);