cleanup: _gnutls_recv_handshake: added explicit sanity checks
Although, this function acts on the message provided as expected and thus it should never call a message parsing function on unexpected messages, we make a more explicit sanity check. This unifies the sanity checks existing within the involved functions.
The existing test suite covers the modified paths, though the fix which is a sanity check should not be exercised by any code path.
Checklist
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Code modified for feature
Reviewer's checklist:
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Any issues marked for closing are addressed -
There is a test suite reasonably covering new functionality or modifications -
Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
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This feature/change has adequate documentation added -
No obvious mistakes in the code