LibJS: Clean up the anonymous wrapper block in "for" using ScopeGuard

This ensures that we don't forget to pop the wrapper off of the scope
stack when returning early due to an exception or some such. :^)

Libraries/LibJS/AST.cpp

@@ -26,6 +26,7 @@
 
 #include <AK/Function.h>
 #include <AK/HashMap.h>
+#include <AK/ScopeGuard.h>
 #include <AK/StringBuilder.h>
 #include <LibJS/AST.h>
 #include <LibJS/Interpreter.h>
@@ -200,6 +201,11 @@ Value ForStatement::execute(Interpreter& interpreter) const
         interpreter.enter_scope(*wrapper, {}, ScopeType::Block);
     }
 
+    auto wrapper_cleanup = ScopeGuard([&] {
+        if (wrapper)
+            interpreter.exit_scope(*wrapper);
+    });
+
     Value last_value = js_undefined();
 
     if (m_init) {
@@ -254,9 +260,6 @@ Value ForStatement::execute(Interpreter& interpreter) const
         }
     }
 
-    if (wrapper)
-        interpreter.exit_scope(*wrapper);
-
     return last_value;
 }