Address reopening https://bugs.kde.org/show_bug.cgi?id=409411#c2 ,

> [...]
> libxslt apparently performs a consistency check on the xmlns URI
> between the stylesheet and the XML input file.
> On the version mismatch, xsltApplyStylesheet() does not return an
> error but silently refuses to carry out the transformations.

umbrello/docgenerators/xmi2docbook.xsl
- In the <xsl:stylesheet> attributes change
                xmlns:UML="http://schema.omg.org/spec/UML/1.3"
  to
                xmlns:UML="http://schema.omg.org/spec/UML/1.4"
  for synchronizing with Umbrello versions since 2.21 (Apps 17.03.80).
- Other changes:
  - Remove whitespace at line ends.
  - Join Xpath expressions spread over two lines to single line.
  - In <xsl:template name="class">,
    - in <xsl:for-each> fix Xpath expression of "select";
    - in <xsl:if test="@xmi.id = $idvalue">,
      - at entity &packagename; <xsl:value-of> fix attribute name in
        "select";
      - in <div role="push">,
        - fix typo at "Abstract";
        - at "Visibility" update ancient <xsl:if> expressions.
  - In <xsl:template name="attribute">,
    - at "Visibility" update ancient <xsl:if> expressions;
    - at "Default" remove non-ASCII/non-UTF8 unidentified characters.
  - In <xsl:template name="operation"> update ancient <xsl:if>
    expressions intended for decoding "visibility".

umbrello/docgenerators/docbookgeneratorjob.cpp
- Enclose additions of commit c6002b5c in #ifdef USE_SDOCBOOK_LOCAL_COPY.
  Reason: The docbook generation appears to function properly without
  them.
- In function run() :
  - Remove local variables for "write the XMI model in an in-memory
    char* string", they appear to be unused.
  - Test return value from xsltParseStylesheetFile(), xmlParseFile(),
    xsltApplyStylesheet() and log an error if null.
  - On freeing up pointers deallocate `cur' last.  Reason: Heap segments
    shall be freed in the opposite order of their allocation.

BUG: 409411
FIXED-IN:2.33.80 (KDE releases 22.03.80)