DOC: update whatsnew/v0.19.1.txt

Author: tsdlovell

doc/source/whatsnew/v0.19.1.txt

@@ -39,6 +39,7 @@ Bug Fixes
 - Bug in ``pd.read_csv`` for Python 2.x in which Unicode quote characters were no longer being respected (:issue:`14477`)
 - Bug in localizing an ambiguous timezone when a boolean is passed (:issue:`14402`)
 - Bug in ``TimedeltaIndex`` addition with a Datetime-like object where addition overflow in the negative direction was not being caught (:issue:`14068`, :issue:`14453`)
+- Bug in ``plot`` where ``NaT`` in ``DatetimeIndex`` results in ``Timestamp.min`` (:issue: `12405`)