Replace upper_bound with lower_bound in pgp_s2k

[evpo]

Fix: RFC4880_encode_count doesn't return consistent results when processing exact iterations. It returns RFC4880 code + 1.

Fixes: #1853

[codecov-io]

Codecov Report

Merging #1854 into master will increase coverage by 1.21%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #1854      +/-   ##
=========================================
+ Coverage   90.18%   91.4%   +1.21%     
=========================================
  Files         527     527              
  Lines       55964   55966       +2     
  Branches     5830    5830              
=========================================
+ Hits        50473   51156     +683     
+ Misses       5491    4810     -681

Impacted Files	Coverage Δ
src/tests/test_pbkdf.cpp	97% <100%> (+0.06%)	⬆️
src/lib/pbkdf/pgp_s2k/pgp_s2k.cpp	87.5% <100%> (ø)	⬆️
src/lib/pk_pad/emsa_raw/emsa_raw.cpp	71.42% <0%> (-2.86%)	⬇️
src/lib/pubkey/mce/mceliece_key.cpp	85.39% <0%> (-1.13%)	⬇️
src/lib/tls/tls_channel.cpp	80.52% <0%> (+0.33%)	⬆️
src/lib/stream/chacha/chacha.cpp	100% <0%> (+0.93%)	⬆️
src/lib/hash/sha2_64/sha2_64.cpp	100% <0%> (+1.11%)	⬆️
src/lib/hash/sha2_32/sha2_32.cpp	98.63% <0%> (+1.36%)	⬆️
src/lib/hash/sha3/sha3.cpp	100% <0%> (+1.44%)	⬆️
src/lib/block/threefish_512/threefish_512.cpp	100% <0%> (+3.12%)	⬆️
... and 8 more

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[randombit]

Sorry about that and thanks for the patch. Can you add something to the test (in test_pbkdf.cpp) that would detect this issue?

[evpo]

No worries, man. I will look at the test.

[evpo]

done