ext/soap: Fix SOAP xsd:hexBinary odd-length decoding

[LamentXU123]

xsd:hexBinary values must contain an even number of hexadecimal digits.

However, previously we allocated strlen(content) / 2 bytes and decoded only complete byte pairs. As a result, an odd-length value such as ABC was accepted as ab (what...?), silently ignoring the trailing nibble.

Lets reject odd-length xsd:hexBinary values instead and throw an Error here which makes better sense. The error message is copied from other decoding errors. (I think in the future, we can make the decoding error message more useful, in bulk.)

 <?php
  class TestSoapClient extends SoapClient {
      public function __doRequest(
          $request,
          $location,
          $action,
          $version,
          $one_way = false,
          ?string $uriParserClass = null
      ): string {
          return <<<'XML'
  <?xml version="1.0" encoding="UTF-8"?>
  <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
                     xmlns:xsd="http://www.w3.org/2001/XMLSchema"
                     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <SOAP-ENV:Body>
      <ns1:testResponse xmlns:ns1="urn:test">
        <return xsi:type="xsd:hexBinary">ABC</return>
      </ns1:testResponse>
    </SOAP-ENV:Body>
  </SOAP-ENV:Envelope>
  XML;
      }
  }

  $client = new TestSoapClient(null, [
      'location' => 'test://',
      'uri' => 'urn:test',
      'exceptions' => true,
  ]);

  var_dump(bin2hex($client->test()));

string(2) "ab"

This is in master as a stricter parsing PR