MXParser failing to parse properly 'encoding' declaration attribute

[belingueres]

Discovered with the help of https://github.com/belingueres/xml-conformance

MXParser fails on parts of the W3C XML Conformance Test Suite.

In this issue, it is failing ibm80n01.xml from "IBM XML Conformance Test Suite - Production 80" (see https://github.com/belingueres/xml-conformance/blob/main/src/test/resources/xmlconf/ibm/ibm_oasis_not-wf.xml) regarding the encoding in the declaration section of the xml file.

[michael-o]

Fixed with a16c27b.