Fixed XML declaration handling in FunctionExternalCommand

* `FunctionExternalCommand` failed to offer correct output handling when provided with a valid XML document which included a XML declaration
** `xerces::XercesDOMParser` generated the appropriate errors but they were not handled by `FunctionExternalCommand`
** wrapping is not necessary for full XML documents but is required for invalid XML as returned by e.g. common _Markdown_ processors
*** if wrapping is applied to full XML documents which include a XML declaration the parser and subsequently the complete external function fails
* added error parser handling by making the compilation unit local `importDocumentElement` method return value optional
* added XML declaration detection and handling to `readOutput`
** if XML declaration is detected no wrapping is applied
* added wrapping detection in `FunctionExternalCommand::constructDocument`
** if no wrapping is detected the whole tree is returned as content instead of just returning its child nodes

1 files changed, 1 insertions, 1 deletions

diff --git a/src/function/base.h b/src/function/base.h
index 34f0a77..5c2d317 100644
--- a/src/function/base.h
+++ b/src/function/base.h
@@ -117,7 +117,7 @@ class FunctionBase : public xalan::Function {
 		template <std::size_t... Index>
 		inline xalan::XalanDocument* callConstructDocument(
 			const XObjectArgVectorType& parameters,
-			const xalan::Locator*       locator,
+			const xalan::Locator*,
 			Sequence<Index...>
 		) const {
 			const FilesystemContext context;