Partially fix safe_parse on formspec version >= 3

README.md

@@ -31,7 +31,7 @@ A Minetest mod library to make modifying formspecs easier.
     pass `formspec` through `formspec_ast.interpret` first.
  - `formspec_ast.safe_parse(string_or_tree)`: Similar to `formspec_ast.parse`,
     however will delete any elements that may crash the client (or any I
-    haven't added to the whitelist).
+    haven't added to the safe element list).
  - `formspec_ast.formspec_escape(text)`: The same as `minetest.formspec_escape`,
     should only be used when formspec_ast is being embedded outside of Minetest.
 

safety.lua

@@ -50,7 +50,7 @@ end
 -- Similar to ast.flatten(), however removes unsafe elements.
 local function safe_flatten(tree)
     local res = {formspec_version = 1}
-    if tree.formspec_version == 2 then
+    if tree.formspec_version and tree.formspec_version > 1 then
         res.formspec_version = 2
     end
     for elem in safe_walk(table.copy(tree)) do