Merge branch 'sb/fix-fetching-moved-submodules'

The code to try seeing if a fetch is necessary in a submodule
during a fetch with --recurse-submodules got confused when the path
to the submodule was changed in the range of commits in the
superproject, sometimes showing "(null)".  This has been corrected.

* sb/fix-fetching-moved-submodules:
  t5526: test recursive submodules when fetching moved submodules
  submodule: fix NULL correctness in renamed broken submodules