PhoneApp: Initialize ToneGenerator when needed

Whenever there is a radio tech change, mSignalInfoToneGenerator
is released and never created. This leads to phone app crash later
when it is accessed for toneplay. This is fixed by creating the
instance (if null) before calling the APIs.

Bug: 8609102
Change-Id: I2f2513624b66892018dc3191daf3e48c63f744a1
Merge "PhoneApp: Initialize ToneGenerator when needed"
Merge branch 'master' into HEAD

Conflicts:
	src/com/android/phone/CallNotifier.java

Change-Id: Ied0a7b93e01018b4df7794c619690466d1b4fc1d