1. Fix the crash in FloatNumberEditorPreference when input null value.
2. Update the input value immediately in NumberPickerPreference.
3. Prevent typing characters in NumberEditorPreference.
Signed-off-by: Pengfei Han <hanpfei@gmail.com>

Change-Id: I16152f2e1f8de386b04ab7a66be8b332b24d0185