Fix issue 34: roxml_del_node() double-free
Fix issue 34: roxml_del_node() double-free

When roxml_add_node an element node with text content as an empty string, be consistent in the condition testing

gergap/libroxml,sartura/libroxml,gergap/libroxml,sartura/libroxml,mahmudur85/libroxml,sartura/libroxml,gergap/libroxml,mahmudur85/libroxml,mahmudur85/libroxml,mahmudur85/libroxml,sartura/libroxml,mahmudur85/libroxml,gergap/libroxml,gergap/libroxml,sartura/libroxml