fix corner case in conditionals (#3669)

fixes #3668

lib/compress.js

@@ -5114,8 +5114,8 @@ merge(Compressor.prototype, {
             var exit = make_node(self.body.CTOR, self, {
                 value: make_node(AST_Conditional, self, {
                     condition   : self.condition,
-                    consequent  : self.body.value || make_node(AST_Undefined, self.body),
-                    alternative : self.alternative.value || make_node(AST_Undefined, self.alternative)
+                    consequent  : self.body.value || make_node(AST_Undefined, self.body).transform(compressor),
+                    alternative : self.alternative.value || make_node(AST_Undefined, self.alternative).transform(compressor)
                 })
             });
             if (exit instanceof AST_Return) {

test/compress/conditionals.js

@@ -1578,3 +1578,34 @@ issue_3576: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3668: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        function f() {
+            try {
+                var undefined = typeof f;
+                if (!f) return undefined;
+                return;
+            } catch (e) {
+                return "FAIL";
+            }
+        }
+        console.log(f());
+    }
+    expect: {
+        function f() {
+            try {
+                var undefined = typeof f;
+                return f ? void 0 : undefined;
+            } catch (e) {
+                return "FAIL";
+            }
+        }
+        console.log(f());
+    }
+    expect_stdout: "undefined"
+}