buf_read_from_tls: Return ERROR_MISC, not WANTWRITE, on BUG().

[nmathewson]

Fixes bug 32673; bugfix on 0.3.0.4-alpha. We introduced these checks in ee5471f9aab5526 to help diagnose 21369, but we used "-1" when "TOR_TLS_ERROR_MISC" would have been correct. Found by opara.

I don't think that this is actually getting triggered in the wild, but if it were, it could cause nasty behavior: spurious WANTREAD/WANTWRITE returns have a way of turning into CPU-eating busy-loops.

[coveralls]

Pull Request Test Coverage Report for Build 7901

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 13 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.02%) to 59.171%

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Files with Coverage Reduction	New Missed Lines	%
src/feature/dirauth/shared_random.c	4	85.1%
src/feature/dirauth/dirvote.c	9	64.65%
<!--	Total:	13

Totals
Change from base Build 7797:	-0.02%
Covered Lines:	43290
Relevant Lines:	73161

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💛 - Coveralls