Fix appwidgets not updating

Previously there was a bug where if an appwidget's update caused a
TransactionTooLargeException then the AppWidgetServiceImpl.Host's
callbacks were completely disabled, for all widgets.

The fix still allows a DeadObjectException or other RemoteException
to disable the host callbacks, as that would be caused by a bad host.

Fixes issue 28216 on the public tracker
https://code.google.com/p/android/issues/detail?id=28216

Change-Id: I5c5d5939d7211ed23cca69e6674de730b51b0f3e
Signed-off-by: Kevin Barry <kevin@teslacoilsw.com>
XmlUtils#readThisMapXml should handle null keys.

Both readThisValueXml & writeThisValueXml have been
implemented to handle values with "null" names.

Change readThisMapXml to allow such names as well, and
map them to the null key in the resulting HashMap.
readThisListXml and readThisSetXml already support
null names.

bug: https://code.google.com/p/android/issues/detail?id=63463

Change-Id: I1c93976656e45e7733113eb67d29b6bad5d25f1f