Add check for uninitialized _sync_dir in DDP Plugin to avoid errors during error handling

[four4fish]

What does this PR do?

python -m pytest -v tests/trainer. passed
python -m pytest -v tests/plugins. passed
python -m pytest -v tests/accelerators. passed

Fixes #9263

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[four4fish]

@ananthsub

[codecov]

Codecov Report

Merging #9267 (7753b4b) into master (f9994d4) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #9267    +/-   ##
=======================================
- Coverage      92%     88%    -4%     
=======================================
  Files         176     178     +2     
  Lines       14810   14854    +44     
=======================================
- Hits        13662   13088   -574     
- Misses       1148    1766   +618