[!250] Fix VariableBlockVector's CreateIterator

Merge branch 'bugfix/fix-vbv-create-iterator' into 'master'

ref:core/dune-istl When the postfix increment operator is used, block sizes
will not be set properly, see [#56].

This implementation places the allocation into the destructor of the iterator.

It does not need additional structures.

This MR also fixes the test for interoperability with STL algorithms: As the
CreateIterator is only an output iterator, use std::fill_n() instead of
std::fill().

See [!249]. Fixes [#56].

See merge request [!250]

  [#56]: gitlab.dune-project.org/NoneNone/issues/56
  [!249]: gitlab.dune-project.org/NoneNone/merge_requests/249
  [!250]: gitlab.dune-project.org/core/dune-istl/merge_requests/250

Closes #56
7 jobs from bugfix/backport-vbvector-createiterator-fix in 2 minutes and 41 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
failed #72380
duneci
debian:10 clang-7-libcpp-17

00:02:20

failed #72379
duneci
debian:10 gcc-8-noassert-17

00:02:41

passed #72382
duneci
debian:9 clang-3.8-14

00:02:14

passed #72381
duneci
debian:9 gcc-6-14

00:02:15

passed #72384
duneci
ubuntu:16.04 clang-3.8-14

00:02:18

passed #72383
duneci
ubuntu:16.04 gcc-5-14

00:02:19

failed #72385
duneci
ubuntu:18.04 clang-6-17

00:02:36

 
Name Stage Failure
failed
debian:10 gcc-8-noassert-17 Test
[ 97%] Linking CXX executable matrixmarkettest
[ 97%] Built target matrixmarkettest
[ 98%] Linking CXX executable iotest
[ 98%] Built target iotest
make[1]: *** [CMakeFiles/Makefile2:1070: CMakeFiles/build_tests.dir/rule] Error 2
make: *** [Makefile:574: build_tests] Error 2
--- Failed to build dune-istl ---
Terminating dunecontrol due to previous errors!
ERROR: Job failed: exit code 1
failed
ubuntu:18.04 clang-6-17 Test
[ 98%] Linking CXX executable iotest
[ 98%] Built target iotest
make[1]: *** [CMakeFiles/build_tests.dir/rule] Error 2
CMakeFiles/Makefile2:1064: recipe for target 'CMakeFiles/build_tests.dir/rule' failed
make: *** [build_tests] Error 2
Makefile:574: recipe for target 'build_tests' failed
--- Failed to build dune-istl ---
Terminating dunecontrol due to previous errors!
ERROR: Job failed: exit code 1
failed
debian:10 clang-7-libcpp-17 Test
[ 98%] Built target pamgtest
13 warnings generated.
[ 98%] Linking CXX executable pamg_comm_repart_test
[ 98%] Built target pamg_comm_repart_test
make[1]: *** [CMakeFiles/Makefile2:1070: CMakeFiles/build_tests.dir/rule] Error 2
make: *** [Makefile:574: build_tests] Error 2
--- Failed to build dune-istl ---
Terminating dunecontrol due to previous errors!
ERROR: Job failed: exit code 1