Fix some slice problems (incorrect slice length) (#19592)

models/auth/oauth2.go

@@ -245,7 +245,7 @@ func deleteOAuth2Application(sess db.Engine, id, userid int64) error {
 		"oauth2_authorization_code.grant_id = oauth2_grant.id AND oauth2_grant.application_id = ?", id).Find(&codes); err != nil {
 		return err
 	}
-	codeIDs := make([]int64, 0)
+	codeIDs := make([]int64, 0, len(codes))
 	for _, grant := range codes {
 		codeIDs = append(codeIDs, grant.ID)
 	}

models/repo_activity.go

@@ -127,7 +127,7 @@ func GetActivityStatsTopAuthors(ctx context.Context, repo *repo_model.Repository
 			user.Commits += v.Commits
 		}
 	}
-	v := make([]*ActivityAuthorData, 0)
+	v := make([]*ActivityAuthorData, 0, len(users))
 	for _, u := range users {
 		v = append(v, u)
 	}

models/user/list.go

@@ -17,7 +17,7 @@ type UserList []*User //revive:disable-line:exported
 
 // GetUserIDs returns a slice of user's id
 func (users UserList) GetUserIDs() []int64 {
-	userIDs := make([]int64, len(users))
+	userIDs := make([]int64, 0, len(users))
 	for _, user := range users {
 		userIDs = append(userIDs, user.ID) // Considering that user id are unique in the list
 	}