fix corner case in inline & sequences (#4718)

fixes #4717

lib/compress.js

@@ -3126,7 +3126,7 @@ merge(Compressor.prototype, {
                 if (prev) {
                     if (stat instanceof AST_Exit) {
                         if (stat.value || !in_async_generator(scope)) {
-                            stat.value = cons_seq(stat.value || make_node(AST_Undefined, stat)).transform(compressor);
+                            stat.value = cons_seq(stat.value || make_node(AST_Undefined, stat)).optimize(compressor);
                         }
                     } else if (stat instanceof AST_For) {
                         if (!(stat.init instanceof AST_Definitions)) {

test/compress/awaits.js

@@ -1246,3 +1246,37 @@ issue_4618: {
     expect_stdout: "function"
     node_version: ">=8"
 }
+
+issue_4717: {
+    options = {
+        inline: true,
+        reduce_vars: true,
+        sequences: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            async function f() {
+                var a = function() {
+                    await;
+                }();
+                return "FAIL";
+            }
+            return f();
+        })().then(console.log).catch(function() {
+            console.log("PASS");
+        });
+    }
+    expect: {
+        (async function() {
+            return function() {
+                await;
+            }(), "FAIL";
+        })().then(console.log).catch(function() {
+            console.log("PASS");
+        });
+    }
+    expect_stdout: "PASS"
+    node_version: ">=8"
+}