Fix for #4150: crash when closing Electron app with custom sync error…

… handler

This follows the pattern from d4d6eab to prevent destruction of the functor

src/js_sync.hpp

@@ -242,6 +242,11 @@ class SyncSessionErrorHandlerFunctor {
         : m_ctx(Context<T>::get_global_context(ctx))
         , m_func(ctx, error_func)
     {
+#if defined(REALM_PLATFORM_NODE)
+        // Suppressing destruct prevents a crash when closing an Electron app with a
+        // custom sync error handler: https://github.com/realm/realm-js/issues/4150
+        m_func.SuppressDestruct();
+#endif
     }
 
     typename T::Function func() const
@@ -289,7 +294,7 @@ class SyncSessionErrorHandlerFunctor {
 
 private:
     const Protected<typename T::GlobalContext> m_ctx;
-    const Protected<typename T::Function> m_func;
+    Protected<typename T::Function> m_func;
 };