The GETINFO extra-info/digest/<digest> broke in commit 568dc27a19 that
refactored the base16_decode() API to return the decoded length.
Unfortunately, that if() condition should have checked for the correct length
instead of an error which broke the command in tor-0.2.9.1-alpha.
Fixes#22034
Signed-off-by: David Goulet <dgoulet@torproject.org>
