[1.10>master] [MERGE #5537 @dilijev] OS#18178361: Don't call JavascriptWeakMap::Clear on shutdown since ScriptContext may have already been freed.

Merge pull request #5537 from dilijev:weakmap-clear

Author: dilijev

lib/Runtime/Library/JavascriptWeakMap.h

@@ -77,7 +77,14 @@ namespace Js
         bool Has(RecyclableObject* key) const;
         void Set(RecyclableObject* key, Var value);
 
-        virtual void Finalize(bool isShutdown) override { Clear(); }
+        virtual void Finalize(bool isShutdown) override
+        {
+            if (!isShutdown)
+            {
+                Clear();
+            }
+        }
+
         virtual void Dispose(bool isShutdown) override { }
 
         virtual BOOL GetDiagTypeString(StringBuilder<ArenaAllocator>* stringBuilder, ScriptContext* requestContext) override;