extdiff: reorder an if-else conditional
This brings continue part on top and will help in next patch where we will like
to introduce utility functions for rest of the code.
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true