Fix AES128 encryption if the OpenSSL extension is installed

[supervirus]

This patch fixes generating of AES128 (mode=2) encrypted PDF files, if the OpenSSL extension is available.

If OpenSSL available TCPDF used aes-256-cbc regardless if mode=2 oder mode=3 was selected - which resulted in an unusable PDF file. Now the functions _AES and _AESnopad use aes-128-cbc or aes-256-cbc depending on the key size.

[codecov-commenter]

Codecov Report

Merging #453 (cbb62dd) into main (172540d) will decrease coverage by 7.44%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
- Coverage   72.93%   65.49%   -7.45%     
==========================================
  Files         127      127              
  Lines       23024    22966      -58     
==========================================
- Hits        16792    15041    -1751     
- Misses       6232     7925    +1693     

Flag	Coverage Δ
php-5.3-ubuntu-latest	45.06% <0.00%> (-27.35%)	:arrow_down:
php-5.4-ubuntu-latest	45.07% <0.00%> (-27.34%)	:arrow_down:
php-5.5-ubuntu-latest	45.07% <0.00%> (-27.34%)	:arrow_down:
php-5.6-ubuntu-latest	45.12% <0.00%> (-0.02%)	:arrow_down:
php-7.1-ubuntu-latest	45.93% <0.00%> (+0.25%)	:arrow_up:
php-7.2-ubuntu-latest	45.89% <0.00%> (+0.26%)	:arrow_up:
php-7.3-ubuntu-latest	45.88% <0.00%> (+0.26%)	:arrow_up:
php-7.4-ubuntu-latest	45.87% <0.00%> (+0.25%)	:arrow_up:
php-8.0-ubuntu-latest	67.24% <0.00%> (+1.89%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
include/tcpdf_static.php	48.02% <0.00%> (-5.52%)	:arrow_down:
examples/example_027.php	61.53% <0.00%> (-37.96%)	:arrow_down:
tcpdf_barcodes_1d.php	60.29% <0.00%> (-30.15%)	:arrow_down:
examples/example_058.php	75.86% <0.00%> (-24.14%)	:arrow_down:
examples/example_039.php	80.64% <0.00%> (-19.36%)	:arrow_down:
tcpdf_barcodes_2d.php	62.98% <0.00%> (-12.99%)	:arrow_down:
tcpdf.php	62.72% <0.00%> (-8.16%)	:arrow_down:
include/tcpdf_colors.php	35.00% <0.00%> (-1.67%)	:arrow_down:
include/tcpdf_fonts.php	43.75% <0.00%> (-1.03%)	:arrow_down:
... and 15 more

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