Fix the issue - Unable to add second VT call when first call is active

- Cache the video state of the new pending call when the foreground
  call is HOLDING.

- Use the cached video state when dialing the pending MO call or
  accepting the pending MT call after the first call is put on HOLD.

Change-Id: I761dcc1e9b8383ea2eb39500873dfa38401268bf
CRs-Fixed: 743214, 741286