fixed vita startup crash by guarding commerce calls

Minecraft.Client/PSVita/PSVita_Minecraft.cpp

@@ -665,7 +665,9 @@ int main()
 	app.CommerceInit(); //  MGH - moved this here so GetCommerce isn't NULL
 
 	// 4J-PB - Kick of the check for trial or full version - requires ui to be initialised
+#ifndef DISABLE_PSN
 	app.GetCommerce()->CheckForTrialUpgradeKey();
+#endif