[Application] application_widget_storage: Add the check for return value.
[Application] application_widget_storage: Add the check for return value.

The return value for GetString() and GetBoolean() was not being checked
in SaveConfigInfoItem().

CID=194012
CID=194029
BUG=XWALK-2928

(cherry picked from commit 8a6bce20e84b84df9e1aa27eb610f16c6f4f1cc5)

TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk,TheDirtyCalvinist/spacewalk