fix: better handle extensions for unrecognized mimetypes #460

Job	Run time
clippy	29s
check	22s
docs	21s
fmt	7s
os-test (ubuntu-latest)	47s
os-test (ubuntu-latest, --no-default-features)	51s
os-test (ubuntu-latest, --all-features)	1m 9s
os-test (windows-latest)	1m 51s
os-test (windows-latest, --no-default-features)	1m 19s
os-test (windows-latest, --all-features)	4m 52s
os-test (macOS-latest)	45s
os-test (macOS-latest, --no-default-features)	41s
os-test (macOS-latest, --all-features)	1m 14s
feature-check	1m 11s
	15m 59s

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