schedrelease() don't schedule if current interrupt frame is NULL

kernel/syscall/sched.c

@@ -11,7 +11,9 @@ int32_t SYSCALL0(sys_schedrelease) {
   Proc *proc = PROCS.current;
   spinlock_release(&PROCS.spinlock);
 
+  if (INTR_CURRENT_FRAME != NULL) {
     proc_sched((void *)INTR_CURRENT_FRAME);
+  }
 
   return E_OK;
 }