revlog: avoid exposing delayed index entry too widely in non-inline revlog

Before this change, the index entry would be seen as "appended" to the data
file. It did not hurt too much as there are never accessed for reading, but this
was odd. So lets stop doing so.

mercurial/revlog.py

@@ -1173,7 +1173,9 b' class _InnerRevlog:'
                 self.opener.unlink(self.index_file)
             return self.index_file
         else:
-            self._segmentfile._delay_buffer = self._delay_buffer = []
+            self._delay_buffer = []
+            if self.inline:
+                self._segmentfile._delay_buffer = self._delay_buffer
             return None
 
     def write_pending(self):
@@ -1193,7 +1195,11 b' class _InnerRevlog:'
                 ifh.seek(0, os.SEEK_END)
                 ifh.write(b"".join(self._delay_buffer))
             any_pending = True
-        self._segmentfile._delay_buffer = self._delay_buffer = None
+        self._delay_buffer = None
+        if self.inline:
+            self._segmentfile._delay_buffer = self._delay_buffer
+        else:
+            assert self._segmentfile._delay_buffer is None
         self._orig_index_file = self.index_file
         self.index_file = pending_index_file
         self._segmentfile.filename = self.index_file