MAINT-1078 Merchant Outbox import failures

Add 1s throttle on update checks for importer
reviewed with Simon

indra/newview/llmarketplacefunctions.cpp

@@ -336,13 +336,19 @@ namespace LLMarketplaceImport
 // Interface class
 //
 
+static const F32 MARKET_IMPORTER_UPDATE_FREQUENCY = 1.0f;
 
 //static
 void LLMarketplaceInventoryImporter::update()
 {
 	if (instanceExists())
 	{
-		LLMarketplaceInventoryImporter::instance().updateImport();
+		static LLTimer update_timer;
+		if (update_timer.hasExpired())
+		{
+			LLMarketplaceInventoryImporter::instance().updateImport();
+			update_timer.setTimerExpirySec(MARKET_IMPORTER_UPDATE_FREQUENCY);
+		}
 	}
 }