fix corner case in unused (#5446)

fixes #5444

lib/compress.js

@@ -7301,6 +7301,13 @@ Compressor.prototype.compress = function(node) {
             }
         }, function(node, in_list) {
             if (node instanceof AST_BlockStatement) return trim_block(node, tt.parent(), in_list);
+            if (node instanceof AST_ExportDeclaration) {
+                var block = node.body;
+                if (!(block instanceof AST_BlockStatement)) return;
+                node.body = block.body.pop();
+                block.body.push(node);
+                return in_list ? List.splice(block.body) : block;
+            }
             if (node instanceof AST_For) return patch_for_init(node, in_list);
             if (node instanceof AST_ForIn) {
                 if (!drop_vars || !compressor.option("loops")) return;