hs-v3: Improve accessor semantic of client cached object

[dgoulet-tor]

Add an inline helper function that indicates if the cached object contains a
decrypted descriptor or not.

The descriptor object is NULL if tor is unable to decrypt it (lacking client
authorization) and some actions need to be done only when we have a decrypted
object.

This improves code semantic.

Fixes #33458

Signed-off-by: David Goulet dgoulet@torproject.org

[coveralls]

Pull Request Test Coverage Report for Build 8439

• 19 of 19 (100.0%) changed or added relevant lines in 1 file are covered.
• 394 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+0.1%) to 63.996%

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Files with Coverage Reduction	New Missed Lines	%
src/feature/dirparse/parsecommon.c	5	87.67%
src/lib/crypt_ops/crypto_rsa.c	7	91.63%
src/lib/crypt_ops/crypto_rsa_openssl.c	10	91.7%
src/feature/dircache/conscache.c	11	93.23%
src/core/or/circuitpadding.c	14	92.24%
src/feature/hs/hs_service.c	60	75.74%
src/feature/relay/relay_config.c	66	74.44%
src/feature/dirauth/process_descs.c	90	42.57%
src/app/config/config.c	131	79.99%

Totals
Change from base Build 8296:	0.1%
Covered Lines:	50697
Relevant Lines:	79219

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💛 - Coveralls