Promise.then non-function callback

src/eval.js

@@ -303,8 +303,8 @@ export const eval_modules = (
         }
         let children_copy = children
 
-        const make_callback = cb => cb == null
-          ? null
+        const make_callback = cb => typeof(cb) != 'function'
+          ? cb
           : value => {
               const current = children
               children = children_copy

test/test.js

@@ -2818,6 +2818,15 @@ const y = x()`
     )
   }),
 
+  test('async/await then non-function', async () => {
+    await assert_code_evals_to_async(
+      `
+        await Promise.resolve(1).then(2)
+      `,
+      1
+    )
+  }),
+
   test('async/await Promise.then creates subcall', async () => {
     const i = await test_initial_state_async(`
       const x = () => 1