Fix Binder Crash due to CellInfo Timeout

When CELL_INFO requests time out at the modem, a
null response is returned so that callers can
differentiate between no cells found and an error.

Bug: 117153084
Test: Manually verified with SL4A by forcing timeout
      with a binder call.

Change-Id: I427550c89d3fe50213c4a3d89be4c476144119e9
1 file changed