util: xml: Enforce return value check from virXMLFormatElement

The function does not transfer errors from 'attrBuf' and 'childBuf'
arguments into 'buf', but rather reports them right away, thus we need
to make sure that it's always checked.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/util/virxml.h

@@ -217,7 +217,8 @@ int
 virXMLFormatElement(virBufferPtr buf,
                     const char *name,
                     virBufferPtr attrBuf,
-                    virBufferPtr childBuf);
+                    virBufferPtr childBuf)
+    ATTRIBUTE_RETURN_CHECK;
 
 struct _virXPathContextNodeSave {
     xmlXPathContextPtr ctxt;