Fix: Use correct methods when writing toposorted structs

If there are other structs in `toposorted_structs` before `strct`, they were written with the methods of `strct` instead of their own. This commit fixes that.

This commit also fixes the check against `out.types.cxx` that should prevent duplicate definitions. I didn't encounter any such issues, but I still think that it makes sense to fix it.

Both issues were introduced in commit 5439fa1.

gen/src/write.rs

@@ -85,10 +85,10 @@ fn write_data_structures<'a>(out: &mut OutFile<'a>, apis: &'a [Api]) {
         match api {
             Api::Struct(strct) if !structs_written.contains(&strct.name.rust) => {
                 for next in &mut toposorted_structs {
-                    if !out.types.cxx.contains(&strct.name.rust) {
+                    if !out.types.cxx.contains(&next.name.rust) {
                         out.next_section();
                         let methods = methods_for_type
-                            .get(&strct.name.rust)
+                            .get(&next.name.rust)
                             .map(Vec::as_slice)
                             .unwrap_or_default();
                         write_struct(out, next, methods);