some corrections of warnings

1 job for master
Status Name Job ID Coverage
failed dune:git--gcc #160


Name Stage Failure
dune:git--gcc Test There is an unknown failure, please try again
make[2]: *** [src/CMakeFiles/navier_stokes.dir/] Error 1
CMakeFiles/Makefile2:1147: recipe for target 'src/CMakeFiles/navier_stokes.dir/all' failed
make[1]: *** [src/CMakeFiles/navier_stokes.dir/all] Error 2
Makefile:160: recipe for target 'all' failed
make: *** [all] Error 2
--- Failed to build dune-amdis ---
Terminating dunecontrol due to previous errors!

ERROR: Build failed: exit code 1