Add and use generics.is_empty() and generics.is_own_empty, rather than using generics' attributes

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -432,7 +432,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
             }
             let gat_generics = tcx.generics_of(gat_def_id);
             // FIXME(jackh726): we can also warn in the more general case
-            if gat_generics.own_params.is_empty() {
+            if gat_generics.is_own_empty() {
                 continue;
             }