[bugfix] Copy the number of rows in the copy constructor.

Due to the latest changes the number of rows was not copied correctly
in all cases.This patch introduces the old behaviour.
Should fix FS #1394.

dune/istl/bcrsmatrix.hh

@@ -754,7 +754,7 @@ namespace Dune {
      * Does a deep copy as expected.
      */
     BCRSMatrix (const BCRSMatrix& Mat)
-      : build_mode(Mat.build_mode), ready(notAllocated), n(0), m(0), nnz(0),
+      : build_mode(Mat.build_mode), ready(notAllocated), n(Mat.n), m(0), nnz(0),
         allocationSize(0), r(0), a(0),
         avg(Mat.avg), overflowsize(Mat.overflowsize)
     {