bug修改

models/statistics/cardcoupon.go

 									) as used_date,
 									(
 										CASE
-										WHEN NOW() > a.end_date THEN
+										WHEN use_date IS NULL and NOW() > a.end_date THEN
 											'expire'
 										WHEN use_date IS NULL THEN
 											'useable'
 									) as used_date,
 									(
 										CASE
-										WHEN NOW() > a.end_date THEN
+										WHEN use_date IS NULL and NOW() > a.end_date THEN
 											'expire'
 										WHEN use_date IS NULL THEN
 											'useable'