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

src/ast/scopes.cc

Index: src/ast/scopes.cc
diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index 1cb3af312d19875ed8c58f927173491f990f6767..404e5075ade835db1469fc6916f4ec0dfe197cd5 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -1508,8 +1508,10 @@ void Scope::Print(int 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) {