Save code now report error for svn type

Monitoring save code now [1] for type svn report error [2] from the worker stacktrace, this looks like an off by one when starting up visits from an already visited repository:

Apr 17 17:07:24 worker2 python3[2637389]: [2021-04-17 17:07:24,952: INFO/ForkPoolWorker-1] Load origin 'https://github.com/cran/SCRABBLE' with type 'svn'
Apr 17 17:07:26 worker2 python3[2637389]: [2021-04-17 17:07:26,765: ERROR/ForkPoolWorker-1] Loading failure, updating to `failed` status
                                          Traceback (most recent call last):
                                            File "/usr/lib/python3/dist-packages/swh/loader/core/loader.py", line 330, in load
                                              self.prepare()
                                            File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 756, in prepare
                                              dump_path = self.dump_svn_revisions(self.svn_url, last_loaded_svn_rev)
                                            File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 741, in dump_svn_revisions
                                              % (last_dumped_rev, last_loaded_svn_rev)
                                          Exception: Last dumped subversion revision (0) is lesser than the last one loaded into the archive (0).

This needs some fixing.

• [2] Ui view

Exception: Last dumped subversion revision (0) is lesser than the last one loaded into the archive (0).

• [1] swh/infra/sysadm-environment#1481 (closed)

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Migrated from T3263 (view on Phabricator)