Fix URL-decoding bug from previous commit

[joka921]

For URL-decoding, now use (the well documented) boost::urls::parse_origin_form instead of the (internal and poorly documented) boost::urls::parse_query because the latter turned out to not unescape + to space.

TODO for a separate PR: When the URL path is malformed, currently a Boost-internal error message is returned, like leftover [boost.url.grammar:4]. Instead an exception should be thrown and caught and a proper error message displayed.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.08%. Comparing base (4c203e2) to head (4118da0). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1517 +/- ## ========================================== - Coverage 92.55% 88.08% -4.48% ========================================== Files 355 355 Lines 26631 26636 +5 Branches 3575 3576 +1 ========================================== - Hits 24649 23463 -1186 - Misses 1940 1947 +7 - Partials 42 1226 +1184 ```

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud