misc: clean up error handling for ext2fs_run_ext3_journal()

misc: clean up error handling for ext2fs_run_ext3_journal()

The ext2fs_run_ext3_journal() function is in debugfs/journal.c, and in
some error conditions cases may close the passed-in file system handle.

Clean up the both the function so that it reliably clears the file
system handle if it has been freed, and its callers so that they do
not crash by dereferencing a null pointer if it has been freed.

Reported-by: Erkki Ruohtula <eru@netti.fi>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>