Catch OSError when source code is not available

[williballenthin]

closes #2468

with this fix, my use case works a bit more:

There's still an outstanding call to getfile but since I haven't hit this code path yet and therefore can't verify a fix, I haven't attempted it.

textual/src/textual/_path.py

Line 30 in c87a2b1

subclass_path = Path(inspect.getfile(obj.__class__))

Please review the following checklist.

• n/a Docstrings on all new or modified functions / classes
• n/a Updated documentation
• Updated CHANGELOG.md (where appropriate)

[willmcgugan]

Seems reasonable.

Do you know if it is possible to detect a FS free environment? i.e. an ENV var?