merge: don't pay for pathconflicts if there are none

mercurial/merge.py

@@ -245,9 +245,12 b' def _checkunknownfiles(repo, wctx, mctx,'
     ):
         backup = (
             f in fileconflicts
-            or f in pathconflicts
+            or pathconflicts
+            and (
+                f in pathconflicts
             or any(p in pathconflicts for p in pathutil.finddirs(f))
         )
+        )
         (flags,) = args
         mresult.addfile(f, mergestatemod.ACTION_GET, (flags, backup), msg)