`UrlUtils::resolveRelativeUrl` wrong result when mixing URLs and absolute paths

[aprat84]

This function doesn't return correct result when the $base is an URL, and the $rel is an absolute path.

You can test with this WSDL, which via imports, ends up trying to load XMLDSig schema, defined in this file which is imported by the WSDL:

<import namespace="http://www.w3.org/2000/09/xmldsig#" schemaLocation="http://www.w3.org/TR/xmldsig-core/xmldsig-core-schema.xsd"/>

Debugging \GoetasWebservices\XML\XSDReader\SchemaReader::loadImport, just before calling UrlUtils::resolveRelativeUrl:

# $namespace 
"http://www.w3.org/2000/09/xmldsig#"
 
# $schemaLocation (from XSD)
"http://www.w3.org/TR/xmldsig-core/xmldsig-core-schema.xsd"

# $schemaLocation (resolved to a known local file and overwritten)
"/var/www/html/vendor/goetas-webservices/xsd-reader/src/Resources/xmldsig-core-schema.xsd"

# $base
"https://prewww2.aeat.es/static_files/common/internet/dep/aplicaciones/es/aeat/tikeV1.0/cont/ws/SistemaFacturacion.wsdl"

So it ends up calling
UrlUtils::resolveRelativeUrl('https://prewww2.aeat.es/static_files/common/internet/dep/aplicaciones/es/aeat/tikeV1.0/cont/ws/SistemaFacturacion.wsdl', '/var/www/html/vendor/goetas-webservices/xsd-reader/src/Resources/xmldsig-core-schema.xsd'), which ends in the file https://prewww2.aeat.es/var/www/html/vendor/goetas-webservices/xsd-reader/src/Resources/xmldsig-core-schema.xsd, which is wrong.

IMHO if $rel is an absolute path, it should just be returned as is. Or treat it differently in \GoetasWebservices\XML\XSDReader\SchemaReader::loadImport.