Enable decoding of unpadded base64 strings

[Regenhardt]

Closes #178

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• [x ] Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the current behaviour?

Pasting a base64 string without the final '=' can not be decoded.

Issue Number: #178

What is the new behaviour?

Pasting a base64 string without final '=' will add the final '=' to the data to be decoded. Input data in the form is not modified.

Other information

Quality check

Before creating this PR, have you:

• [x ] Followed the code style guideline as described in CONTRIBUTING.md
• Verified that the change work in Release build configuration // Storage full, currently can't build
• [x ] Checked all unit tests pass

[Regenhardt]

Turns out installing VS2022 side-by-side and a few new modules filled up my storage real good. Will check that box when I cleaned up.

[veler]

Actually, it seems like some unit tests don't pass anymore, according to the CI? 🤔

unit tests are failing

[Regenhardt]

Oh damn, I'm glad I wrote that test lol.
So let's make sure I got it right this time:
if I'm 3 over, length%4 is 3, and I want one padding to land on the 4 exactly, so padding has to be 4-3=1. Seems to fit my code.

[Regenhardt]

So it works fine locally, and also the failed test has nothing to do with this feature or my changes. Not sure how to fix that.

[Regenhardt]

Rebased onto main, let's see what happens I guess.

[Regenhardt]

Yup rebase worked, this one's ready now.

[veler]

Hello,
Sorry for the late answer.
All the tests pass now :) Thank you very much for this contribution! :D