Remove raising of unreachable error

Author: howsiwei

pandas/tseries/offsets.py

@@ -738,11 +738,11 @@ def rollforward(self, dt):
         return dt
 
     def _get_closing_time(self, dt):
+        # dt is guaranteed to be a starting time
         for i, st in enumerate(self.start):
             if st.hour == dt.hour and st.minute == dt.minute:
                 return dt + timedelta(
                     seconds=self._get_business_hours_by_sec(st, self.end[i]))
-        raise ValueError("dt should be a starting time")
 
     @apply_wraps
     def apply(self, other):