issue #43: AttributeError instances might not have a .obj

[cfbolz]

deal with this situation without crashing, AttributeError.obj is only always there after 3.10

[coveralls]

Pull Request Test Coverage Report for Build 3469906991

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 120 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.5%) to 65.463%

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Files with Coverage Reduction	New Missed Lines	%
/opt/hostedtoolcache/Python/3.10.8/x64/lib/python3.10/site-packages/exceptiongroup/_formatting.py	10	91.83%
/opt/hostedtoolcache/PyPy/3.8.13/x64/lib/pypy3.8/site-packages/exceptiongroup/_formatting.py	22	17.32%
/opt/hostedtoolcache/Python/3.11.0/x64/lib/python3.11/site-packages/exceptiongroup/_formatting.py	22	0%
/opt/hostedtoolcache/Python/3.7.15/x64/lib/python3.7/site-packages/exceptiongroup/_formatting.py	22	69.41%
/opt/hostedtoolcache/Python/3.8.14/x64/lib/python3.8/site-packages/exceptiongroup/_formatting.py	22	69.61%
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/exceptiongroup/_formatting.py	22	69.61%

Totals
Change from base Build 3464999418:	0.5%
Covered Lines:	2049
Relevant Lines:	3130

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💛 - Coveralls