Fix crash in --print-scopes when Scope::variables_ is empty

src/ast/scopes.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/scopes.h"
 
 #include <set>
 
 #include "src/accessors.h"
 #include "src/ast/ast.h"
@@ skipping 1490 matching lines @@
     Indent(n1, "// ");
     PrintF("%d heap slots\n", num_heap_slots_);
   }
 
   // Print locals.
   if (function != nullptr) {
     Indent(n1, "// function var:\n");
     PrintVar(n1, function);
   }
 
-  PrintMap(n1, "// local vars:\n", &variables_, true, function);
-  PrintMap(n1, "// dynamic vars:\n", &variables_, false, function);
+  if (variables_.occupancy() > 0) {
+    PrintMap(n1, "// local vars:\n", &variables_, true, function);
+    PrintMap(n1, "// dynamic vars:\n", &variables_, false, function);
+  }
 
   // Print inner scopes (disable by providing negative n).
   if (n >= 0) {
     for (Scope* scope = inner_scope_; scope != nullptr;
          scope = scope->sibling_) {
       PrintF("\n");
       scope->Print(n1);
     }
   }
 
@@ skipping 541 matching lines @@
   Variable* function =
       is_function_scope() ? AsDeclarationScope()->function_var() : nullptr;
   bool is_function_var_in_context =
       function != nullptr && function->IsContextSlot();
   return num_heap_slots() - Context::MIN_CONTEXT_SLOTS -
          (is_function_var_in_context ? 1 : 0);
 }
 
 }  // namespace internal
 }  // namespace v8