zodbcommit: Don't forget to call tpc_abort on an error

Two-phase commit protocol assumes that after tpc_begin, it will be
either successful tpc_vote + tpc_finish, or tpc_abort. We were not
calling tpc_abort on an error, potentially leaving storage in "commit is
in progress" state on an error.

/reviewed-by @jerome
/reviewed-on !19

zodbtools/zodbcommit.py

-# Copyright (C) 2018-2020  Nexedi SA and Contributors.
+# Copyright (C) 2018-2021  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -58,6 +58,8 @@ def zodbcommit(stor, at, txn):
     before = p64(u64(at)+1)
 
     stor.tpc_begin(txn)
+
+    def _():
         for obj in txn.objv:
             data = None # data do be committed - setup vvv
             if isinstance(obj, zodbdump.ObjectCopy):
@@ -100,7 +102,12 @@ def zodbcommit(stor, at, txn):
             else:
                 stor.store(obj.oid, serial_prev, data, '', txn)
 
+    try:
+        _()
         stor.tpc_vote(txn)
+    except:
+        stor.tpc_abort(txn)
+        raise
 
     # in ZODB >= 5 tpc_finish returns tid directly, but on ZODB 4 it
     # does not do so. Since we still need to support ZODB 4, utilize tpc_finish