bashlib/ocrd_wrap_cli_processor: show help if METS does not exist

[kba]

#438, OCR-D/spec#156

[codecov-commenter]

Codecov Report

Merging #503 into master will decrease coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #503      +/-   ##
==========================================
- Coverage   80.37%   80.27%   -0.10%     
==========================================
  Files          49       41       -8     
  Lines        2797     2515     -282     
  Branches      544      487      -57     
==========================================
- Hits         2248     2019     -229     
+ Misses        446      408      -38     
+ Partials      103       88      -15     

Impacted Files	Coverage Δ
ocrd/ocrd/decorators.py	95.12% <100.00%> (+15.12%)	⬆️
ocrd_utils/ocrd_utils/__init__.py	66.01% <0.00%> (-33.99%)	⬇️
ocrd/ocrd/cli/workspace.py	68.86% <0.00%> (-2.86%)	⬇️
ocrd/ocrd/workspace.py	58.02% <0.00%> (-2.24%)	⬇️
ocrd/ocrd/cli/process.py	75.00% <0.00%> (-1.93%)	⬇️
ocrd_models/ocrd_models/ocrd_mets.py	92.07% <0.00%> (-1.06%)	⬇️
..._validators/ocrd_validators/workspace_validator.py	84.61% <0.00%> (-0.55%)	⬇️
ocrd_models/ocrd_models/ocrd_file.py	90.90% <0.00%> (-0.27%)	⬇️
ocrd/ocrd/cli/__init__.py	100.00% <0.00%> (ø)
ocrd_utils/ocrd_utils/constants.py	100.00% <0.00%> (ø)
... and 16 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f9dd047...2f7caf0. Read the comment docs.