update: random coupon minus point method

Author: vumrra

src/main/kotlin/gogo/gogostage/domain/coupon/root/application/CouponProcessor.kt

@@ -56,7 +56,7 @@ class CouponProcessor(
         if (isGain) {
             participant.plusPoint(coupon.earnPoint)
         } else {
-            participant.minusPoint(coupon.lostPoint!!)
+            participant.minusPointMust(coupon.lostPoint!!)
         }
     }
 

src/main/kotlin/gogo/gogostage/domain/stage/participant/root/persistence/StageParticipant.kt

@@ -46,6 +46,15 @@ class StageParticipant(
         this.point -= point
     }
 
+    fun minusPointMust(point: Long) {
+        if (this.point - point < 0) {
+            this.point = 0
+            return
+        }
+
+        this.point -= point
+    }
+
     fun plusPoint(point: Long) {
         this.point += point
     }