fix PKESKv6 PQC encryption case

[TJ-91]

Fixes #63

CLI Tests still have an error but I believe that's unrelated:

285: ERROR: test_zzz_encryption_and_signing_pqc (__main__.Encryption)
285: ----------------------------------------------------------------------
285: Traceback (most recent call last):
285:   File "/home/jroth/PQC_TB/rnp-dev/src/tests/cli_tests.py", line 4501, in test_zzz_encryption_and_signing_pqc
285:     signerpws = [passwds[i]]
285: IndexError: list index out of range
285: 

@falko-strenzke Should I still implement a unit test for PQC encryption (that would've caught this), or is it enough to have the CLI test now?

[falko-strenzke]

Fixes #63

CLI Tests still have an error but I believe that's unrelated:

285: ERROR: test_zzz_encryption_and_signing_pqc (__main__.Encryption)
285: ----------------------------------------------------------------------
285: Traceback (most recent call last):
285:   File "/home/jroth/PQC_TB/rnp-dev/src/tests/cli_tests.py", line 4501, in test_zzz_encryption_and_signing_pqc
285:     signerpws = [passwds[i]]
285: IndexError: list index out of range
285: 

@falko-strenzke Should I still implement a unit test for PQC encryption (that would've caught this), or is it enough to have the CLI test now?

If we don't have a unit-test for pqc encryption, then yes, I think we should implement one.