Update src/simulation/m_time_steppers.fpp

Co-authored-by: qodo-merge-pro[bot] <151058649+qodo-merge-pro[bot]@users.noreply.github.com>

Author: hyeoksu-lee

src/simulation/m_time_steppers.fpp

@@ -522,7 +522,7 @@ contains
                 do l = 0, p
                     do k = 0, n
                         do j = 0, m
-                            if (s == 1 .and. time_stepper /= 1) then
+                            if (s == 1 .and. nstage > 1) then
                                 q_cons_ts(stor)%vf(i)%sf(j, k, l) = &
                                     q_cons_ts(1)%vf(i)%sf(j, k, l)
                             end if