xml BUGFIX asigning namespace to the elements

sometimes, a correctly assigned namespace (defined in the node) was
replaced by different (wrong) namespace inherited from parent.
diff --git a/src/xml.c b/src/xml.c
index dfedb99..b22514c 100644
--- a/src/xml.c
+++ b/src/xml.c
@@ -1055,7 +1055,7 @@
         goto error;
     }
 
-    if (!nons_flag && parent) {
+    if (!elem->ns && !nons_flag && parent) {
         elem->ns = get_ns(parent, prefix_len ? prefix : NULL);
     }