Settings: check if NfcAdapter is null

according to the javadoc, getDefaultAdapter(Context) can return null, if
no NFC adapter exists.

check if adapter is null before trying to call isEnabled

Change-Id: I7ff5488cc3b53ce9785c3e46effcf29dc31fe0ef

Conflicts:
	src/com/android/settings/Settings.java
Show "Eject card" for usb storage

Readd the "Eject" options if the SD card is mounted via usb.

Change-Id: I802cf4d20eb3b45ce068f89c22352f79999d593e