Fixup feature(never_type_fallback) handling

Author: WaffleLapkin

compiler/rustc_hir_typeck/src/fallback.rs

@@ -100,6 +100,10 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             .get_attr(CRATE_DEF_ID, sym::rustc_never_type_mode)
             .map(|attr| (attr.value_str().unwrap(), attr.span))
         else {
+            if self.tcx.features().never_type_fallback {
+                return DivergingFallbackBehavior::FallbackToNiko;
+            }
+
             return DivergingFallbackBehavior::FallbackToUnit;
         };