fix a corner case in #1530 (#1552)

test/compress/functions.js

@@ -74,3 +74,20 @@ iifes_returning_constants_keep_fargs_false: {
         console.log((a(), b(), 6));
     }
 }
+
+issue_485_crashing_1530: {
+    options = {
+        conditionals: true,
+        dead_code: true,
+        evaluate: true,
+    }
+    input: {
+        (function(a) {
+            if (true) return;
+            var b = 42;
+        })(this);
+    }
+    expect: {
+        this, void 0;
+    }
+}