fileset: fix generator vs list bug in fast path
$ hg debugfileset 'a or b'
would only return a or b but not both because the base file list was a
generator instead of a replayable sequence.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state