revlog: adapt the `reading` check for `bundlerepo`

We cannot just rely on the length check for the `bundlerepo` as the local
revlog might be empty with all data in the bundle.

mercurial/bundlerepo.py

@@ -12,6 +12,7 b' were part of the actual repository.'
 """
 
 
+import contextlib
 import os
 import shutil
 
@@ -108,6 +109,14 b' class bundlerevlog(revlog.revlog):'
             self.bundlerevs.add(n)
             n += 1
 
+    @contextlib.contextmanager
+    def reading(self):
+        if self.repotiprev < 0:
+            yield
+        else:
+            with super().reading() as x:
+                yield x
+
     def _chunk(self, rev, df=None):
         # Warning: in case of bundle, the diff is against what we stored as
         # delta base, not against rev - 1