revlog: add a fast path for "ambiguous identifier" Before fd1bb7c, if the C index.partialmatch raises RevlogError, the Python code raises "ambiguous identifier" error immediately, which is efficient. fd1bb7c took hidden revisions into consideration and forced the slow path enumerating the changelog to double-check hidden revisions. But it's not necessary if we know the revlog has no hidden revisions. This patch adds back the fast path for unfiltered revlogs.