autofree: do not free tmp vars twice

Author: medvednikov

vlib/v/gen/cgen.v

@@ -1971,6 +1971,9 @@ fn (mut g Gen) autofree_var_call(free_fn_name string, v ast.Var) {
 		// tmp expr vars do not need to be freed again here
 		return
 	}
+	if v.is_autofree_tmp {
+		return
+	}
 	if v.typ.is_ptr() {
 		g.writeln('\t${free_fn_name}(${c_name(v.name)}); // autofreed ptr var')
 	} else {