fix corner case in loops (#4565)

fixes #4564

test/compress/loops.js

@@ -1280,3 +1280,33 @@ issue_4355: {
     }
     expect_stdout: "PASS"
 }
+
+issue_4564: {
+    options = {
+        loops: true,
+        unused: true,
+    }
+    input: {
+        try {
+            throw null;
+        } catch (a) {
+            var a;
+            (function() {
+                for (a in "foo");
+            })();
+            console.log(a);
+        }
+    }
+    expect: {
+        try {
+            throw null;
+        } catch (a) {
+            var a;
+            (function() {
+                for (a in "foo");
+            })();
+            console.log(a);
+        }
+    }
+    expect_stdout: "2"
+}

test/reduce.js

@@ -666,7 +666,7 @@ function has_loopcontrol(body, loop, label) {
 }
 
 function is_error(result) {
-    return typeof result == "object" && typeof result.name == "string" && typeof result.message == "string";
+    return result && typeof result.name == "string" && typeof result.message == "string";
 }
 
 function is_timed_out(result) {