fix: fix crash when disable fast trading

Author: pynickle

common/src/main/java/com/euphony/better_client/mixin/MerchantScreenMixin.java

@@ -67,10 +67,10 @@ public void addSpeedTradeButton(CallbackInfo ci) {
     protected void containerTick() {
         super.containerTick();
 
-        this.better_client$fastTradingButton.active = false;
-
         if(!config.enableFastTrading) return;
 
+        this.better_client$fastTradingButton.active = false;
+
         Inventory inventory;
         if (this.minecraft != null) {
             if (this.minecraft.player != null) {