Doc fix: QDomDocument::ParseResult is false on error

The documentation claimed the exact opposite of what the
implementation did. Since callers use it the way it's implemented, fix
the doc.

Fixes: QTBUG-112895
Pick-to: 6.6 6.5
Change-Id: I74d6259727c7af7265224c6d79ba39265663704b
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/xml/dom/qdom.cpp

@@ -6336,8 +6336,8 @@ QT_WARNING_POP
 /*!
     \fn QDomDocument::ParseResult::operator bool() const
 
-    Returns \c true if an error is found by QDomDocument::setContent();
-    otherwise returns \c false.
+    Returns \c false if any error is found by QDomDocument::setContent();
+    otherwise returns \c true.
 
     \sa QDomDocument::setContent()
 */