fix unused patching of AST_For.init blocks (#2289)

fixes #2288

lib/compress.js

@@ -2423,17 +2423,18 @@ merge(Compressor.prototype, {
                 // We fix it at this stage by moving the `var` outside the `for`.
                 if (node instanceof AST_For) {
                     descend(node, this);
+                    var block;
                     if (node.init instanceof AST_BlockStatement) {
-                        var block = node.init;
+                        block = node.init;
                         node.init = block.body.pop();
                         block.body.push(node);
-                        return in_list ? MAP.splice(block.body) : block;
+                    }
-                    } else if (node.init instanceof AST_SimpleStatement) {
+                    if (node.init instanceof AST_SimpleStatement) {
                         node.init = node.init.body;
                     } else if (is_empty(node.init)) {
                         node.init = null;
                     }
-                    return node;
+                    return !block ? node : in_list ? MAP.splice(block.body) : block;
                 }
                 if (node instanceof AST_LabeledStatement && node.body instanceof AST_For) {
                     descend(node, this);

test/compress/drop-unused.js

@@ -1239,3 +1239,25 @@ issue_2226_3: {
     }
     expect_stdout: "3"
 }
+
+issue_2288: {
+    options = {
+        unused: true,
+    }
+    beautify = {
+        beautify: true,
+    }
+    input: {
+        function foo(o) {
+            for (var j = o.a, i = 0; i < 0; i++);
+            for (var i = 0; i < 0; i++);
+        }
+    }
+    expect: {
+        function foo(o) {
+            o.a;
+            for (i = 0; i < 0; i++);
+            for (var i = 0; i < 0; i++);
+        }
+    }
+}