Quick fix for a len() of unsized object problem.

Not sure why this happens.

src/ZODB/fsdump.py

@@ -74,6 +74,10 @@ def fsdump(path, file=None, with_offset=1):
                 bp = ""
             if rec.data_txn:
                 size = 8 + len(rec.version)
+            else:
+                if rec.data is None:
+                    # XXX why is rec.data None and rec.data_txn False?
+                    size = len(rec.version)
                 else:
                     size = len(rec.data) + len(rec.version)
             if rec.version: