We weren't checking whether the request creating the proposal had
finished before checking the document. That's probably why this test has
recently failed on our CI:
```
1) Documents Metadata download document without metadata
Failure/Error: io = URI.parse(
"#{app_host}#{polymorphic_path(
Document.last.attachment)}"
).open
NoMethodError:
undefined method `attachment' for nil:NilClass
```
98fec3bb2f