### Please describe the problem.

git-annex does not report percent-progress in the json-progress output if size is not listed in the key.  But the file is available so git annex could easily report the %s.  We will need to workaround in datalad atm where we assumed that percents are always reported

[[!format sh """
$> git annex copy --to=localhost --json --json-progress Why_is_git_annex_awesome__This_is_why_.webm 
{"byte-progress":32768,"action":{"command":"copy","note":"to localhost...","key":"URL--quvi:https://www.youtube.com/watch,63v,614qCZFW_uGU0","file":"Why_is_git_annex_awesome__This_is_why_.webm"}}
{"command":"copy","note":"to localhost...","success":true,"key":"URL--quvi:https://www.youtube.com/watch,63v,614qCZFW_uGU0","file":"Why_is_git_annex_awesome__This_is_why_.webm"}

$> du -scmL Why_is_git_annex_awesome__This_is_why_.webm
6	Why_is_git_annex_awesome__This_is_why_.webm
6	total

$> git annex version
git-annex version: 6.20171018+gitgbb20b1ed3-1~ndall+1
...

$> ls -l Why_is_git_annex_awesome__This_is_why_.webm
lrwxrwxrwx 1 yoh yoh 150 Nov  3 09:02 Why_is_git_annex_awesome__This_is_why_.webm -> ../../.git/annex/objects/8f/XP/URL--quvi&chttps&c%%www.youtube.com%watch,63v,614qCZFW_uGU0/URL--quvi&chttps&c%%www.youtube.com%watch,63v,614qCZFW_uGU0

"""]]

> [[done]], but see my caveat about needing to handle lack of progress
> output anyway. --[[Joey]]
