priority: be backwards compatible with priority strings starting with NONE
That is, we allow priority strings which do not enable any groups to work, by disabling TLS1.3. For example 'NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-GCM:+SIGN-ALL:+COMP-NULL' is still operational, but no TLS1.3 is enabled when specified.
Checklist
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Code modified for feature -
Test suite updated with functionality tests
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
Edited by Nikos Mavrogiannopoulos