parse_revid - Badarg error in HTTP request

Does revid have some undocumented limitation? couchdb 1.7.1

```
[error] [<0.11900.1269>] Badarg error in HTTP request
["MeGVONcBrkF5jQ-_ingest_scheduler",16],
[]},
{couch_doc,parse_revid,1,
[{file,"couch_doc.erl"},{line,163}]},
{couch_doc,
'-transfer_fields/2-lc$^1/1-1-',1,
[{file,"couch_doc.erl"},{line,283}]},
{couch_doc,
'-transfer_fields/2-lc$^1/1-1-',1,
[{file,"couch_doc.erl"},{line,283}]},
{couch_doc,transfer_fields,2,
[{file,"couch_doc.erl"},{line,283}]},
{couch_httpd_db,'-db_req/2-fun-3-',1,
[{file,"couch_httpd_db.erl"},
{line,345}]},
{lists,map,2,
[{file,"lists.erl"},{line,1237}]},
{couch_httpd_db,db_req,2,
[{file,"couch_httpd_db.erl"},
{line,344}]}]
```

Start with couch_doc.erl at parse_revid/1 line 163, then follow transfer_fields/2 at line 283 and the couch_httpd_db db_req path around lines 344-345. Reproduce the HTTP request containing the shown revid and determine whether it violates an input limitation; done when the limitation and appropriate handling are clearly established.

Written by the indexing model from the issue text.