Description of problem:
Running "duplicity --full-if-older-than 32D --encrypt-key <key> /backup/ sftp://backup.net//backup-offsite/ --use-agent" ends up with this failure which feels like a bug:

--- snipp ---
Local and Remote metadata are synchronized, no sync needed.
Last inc backup left a partial set, restarting.
Last full backup date: Mon Aug 19 01:00:02 2019
RESTART: Volumes 68 to 68 failed to upload before termination.
         Restarting backup at volume 68.
Restarting after volume 67, file server/gitlab/gitlab-Incremental-0251, block 8176
/usr/lib64/python2.7/site-packages/duplicity/util.py:79: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6
  m = e.message
Traceback (innermost last):
  File "/usr/bin/duplicity", line 1581, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1567, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1419, in main
    do_backup(action)
  File "/usr/bin/duplicity", line 1549, in do_backup
    incremental_backup(sig_chain)
  File "/usr/bin/duplicity", line 673, in incremental_backup
    globals.backend)
  File "/usr/bin/duplicity", line 435, in write_multivol
    globals.volsize)
  File "/usr/lib64/python2.7/site-packages/duplicity/gpg.py", line 386, in GPGWriteFile
    data = block_iter.next().data
  File "/usr/lib64/python2.7/site-packages/duplicity/diffdir.py", line 523, in next
    result = self.process(self.input_iter.next())
  File "/usr/lib64/python2.7/site-packages/duplicity/diffdir.py", line 218, in get_delta_iter
    (new_path, sig_path, sigTarFile))
  File "/usr/lib64/python2.7/site-packages/duplicity/robust.py", line 38, in check_common_error
    return function(*args)
  File "/usr/lib64/python2.7/site-packages/duplicity/diffdir.py", line 139, in get_delta_path
    delta_path.setfileobj(librsync.DeltaFile(old_sigfp, newfp))
  File "/usr/lib64/python2.7/site-packages/duplicity/librsync.py", line 159, in __init__
    self.maker = _librsync.new_deltamaker(sig_string)
 OverflowError: size does not fit in an int
--- snapp ---

Version-Release number of selected component (if applicable):
duplicity-0.7.19-1.el7.x86_64

How reproducible:
Currently all the time, but not sure how it is triggered.

Actual results:
Duplicity fails with "OverflowError: size does not fit in an int"

Expected results:
No Python traceback failure. If at all, a properly catched failure, which is user/admin friendly.