remotefilelog: correctly reject wdir filenodes
This fixes `hg grep -r 'wdir()'` when remotefilelog is enabled and the working
directory contains uncommitted modifications.
Differential Revision: https://phab.mercurial-scm.org/D6217
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"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
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