fix: remove unwanted '\0' string terminator from argument's value

[airween]

what

This PR removes the unwanted \0 character from the end of parsed argument value, if the SecParseXmlIntoArgs feature is enabled and if the node is empty.

why

Now if the node is empty the engine adds an extra byte to the argument's value, which is the string terminator. That character will be part of the value, so if the node is <foo></foo>, the value will be \0 with length 1. Then the parsed argument will be xml.foo=\x00 - which can cause false positives.

[airween]

Cc: @RedXanadu

[sonarqubecloud]

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 SonarQube Cloud

[RedXanadu]

I've tested this over the past few days and can confirm this PR resolves the issue where stray null characters were appearing in ARGS and causing lots of false positives.

No false positives and no unexpected null chars after applying this change.