telephony: SignalStrengh: Don't calculate a LTE snr if the srq is invalid

If the previous values are invalid and signal quality is -1, chances are there's
no LTE signal at all, so don't calculate the SNR and mark it invalid as well.

This fixes the strength indicator in GSM devices where it was being skewed
by the ghost LTE value

Change-Id: I070573401c141aa99941a332ee256246697abb90
Frameworks: icon materialization

These are the first few. There are still 23 more shortcut image
        resources that need to be done, and these will come
        sometime next week probably.

Change-Id: Ie10d154914d2e4cfe2e7960791cff6240a1a2765