workingctx: build _manifest on filenode() or flags() request
I'm not sure if this is the best workaround, but this fixes the following
exception:
AttributeError: 'workingctx' object has no attribute '_manifestdelta'
The short hash '303030303030' seen in the test is node.modifiednodeid.
Differential Revision: https://phab.mercurial-scm.org/D2940
{header}
<!-- Error -->
<id>{urlbase}{url|urlescape}</id>
<link rel="self" href="{urlbase}{url|urlescape}atom-log"/>
<link rel="alternate" href="{urlbase}{url|urlescape}"/>
<title>Error</title>
<updated>1970-01-01T00:00:00+00:00</updated>
<entry>
<title>Error</title>
<id>https://mercurial-scm.org/#error</id>
<author>
<name>mercurial</name>
</author>
<updated>1970-01-01T00:00:00+00:00</updated>
<content type="text">{error|escape}</content>
</entry>
</feed>