Actually fix the memory leak in debugger wrt promises.

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index b4421d6df8f2ffa51ce10a8f35d7b955bf4b3a99..80f993b82b29ecceee5c98e7a50644b9e75feec1 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -807,15 +807,15 @@ bool Debug::Load() {
 void Debug::Unload() {
   ClearAllBreakPoints();
 
+  // Match unmatched PromiseHandlePrologue calls.
+  while (thread_local_.promise_on_stack_) PromiseHandleEpilogue();
+
   // Return debugger is not loaded.
   if (!IsLoaded()) return;
 
   // Clear the script cache.
   DestroyScriptCache();
 
-  // Match unmatched PromiseHandlePrologue calls.
-  while (thread_local_.promise_on_stack_) PromiseHandleEpilogue();
-
   // Clear debugger context global handle.
   GlobalHandles::Destroy(Handle<Object>::cast(debug_context_).location());
   debug_context_ = Handle<Context>();