Initialize the buffer

Initialize the char array to null character
as there is a possibility that it is not null
terminated.

Change-Id: If1eca2b2f3ec22bafeb303da02deb62f0655241c
CRs-Fixed: 584311
Use SimRefreshResponse struct in RIL Versions greater than 7.

Modify condition to use SimRefreshResponse struct in
all RIL Versions greater than 7.

CRs-Fixed: 597007

Change-Id: I40fb4ad96e191ae6641eb31da014515d08704382