[libxml2] Fix error code in xmlTextWriterStartDocument

[Nick Wellnhofer <nwellnhof src gnome org>]

commit d8999b1da03006390f22a4dc8fafcbbab92f3594
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Oct 14 17:04:04 2019 +0200

    Fix error code in xmlTextWriterStartDocument
    
    Return XML_ERR_UNSUPPORTED_ENCODING if no encoding handler could be
    found.
    
    Fixes bug #521808:
    https://bugzilla.gnome.org/show_bug.cgi?id=521808
    
    Resolves !53.

 xmlwriter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/xmlwriter.c b/xmlwriter.c
index 58ffab63..58445c84 100644
--- a/xmlwriter.c
+++ b/xmlwriter.c
@@ -541,8 +541,8 @@ xmlTextWriterStartDocument(xmlTextWriterPtr writer, const char *version,
     if (encoding != NULL) {
         encoder = xmlFindCharEncodingHandler(encoding);
         if (encoder == NULL) {
-            xmlWriterErrMsg(writer, XML_ERR_NO_MEMORY,
-                            "xmlTextWriterStartDocument : out of memory!\n");
+            xmlWriterErrMsg(writer, XML_ERR_UNSUPPORTED_ENCODING,
+                            "xmlTextWriterStartDocument : unsupported encoding\n");
             return -1;
         }
     }