avoid double-copy

Author: jbrockmendel

pandas/core/arrays/timedeltas.py

@@ -243,12 +243,14 @@ def astype(self, dtype, copy=True):
             # by pandas convention, converting to non-nano timedelta64
             #  returns an int64-dtyped array with ints representing multiples
             #  of the desired timedelta unit.  This is essentially division
-            result = self._data.astype(dtype, copy=copy)
             if self._hasnans:
+                # avoid double-copying
+                result = self._data.astype(dtype, copy=False)
                 values = self._maybe_mask_results(result,
                                                   fill_value=None,
                                                   convert='float64')
                 return values
+            result = self._data.astype(dtype, copy=copy)
             return result.astype('i8')
         elif is_timedelta64_ns_dtype(dtype):
             if copy: