Element.vala: fix issue with freeing xmlAttr memory; don't be overzealous,...

Element.vala: fix issue with freeing xmlAttr memory; don't be overzealous, only free when we'd lose out-of-tree references; in-tree will be handled by xmlFreeDoc

gxml/Element.vala

@@ -156,12 +156,18 @@ namespace GXml {
 						saved_attr = this.node->set_prop (propname, attr.node_value);
 					}
 
-					// Replace the old out-of-tree attr with the newly allocated one in the tree, that way xmlFreeDoc can clean up correctly
+					/* Replace an old out-of-tree attr with the newly
+					 * allocated one in the tree, that way xmlFreeDoc can
+					 * clean up correctly */
+					if (attr.node->parent == null) {
+						/* If it was in-tree, xmlSetProp should correctly handle the
+						   memory when updating the value within its xmlAttr */
 						attr.node->free ();
 						attr.node = saved_attr;
 					}
 				}
 			}
+		}
 
 
 		/* Constructors */