edge case fix for type references enums and unions enums

[kflemin]

• Fixes #156

[coveralls]

Pull Request Test Coverage Report for Build 1689781762

• 67 of 81 (82.72%) changed or added relevant lines in 1 file are covered.
• 269 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.005%) to 43.254%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bsyncviewer/lib/schema_parser.py	67	81	82.72%
<!--	Total:	67	81	82.72%	-->

Files with Coverage Reduction	New Missed Lines	%
.tox/python/lib/python3.6/site-packages/urllib3/util/connection.py	16	31.94%
.tox/python/lib/python3.6/site-packages/urllib3/util/retry.py	86	31.4%
.tox/python/lib/python3.6/site-packages/urllib3/connectionpool.py	167	19.17%
<!--	Total:	269		-->

Totals
Change from base Build 1668177783:	0.005%
Covered Lines:	39276
Relevant Lines:	90803

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💛 - Coveralls