hero-common: libril: avoid SEGV when requesting call forwarding info

libsec-ril.so crashes when requesting call forwarding info.  The reason
is that Samsung's RIL_CallForwardInfo has two extra members, string
pointers called startTime and endTime.   There's no such thing as start
and end time defined for GSM call forwarding, so it's not clear what's
the purpose.  However, adding these members to RIL_CallForwardInfo
and setting them to NULL fixes the crash.

Change-Id: I174bb24996e79c378a94921f105168f6c574a044
Signed-off-by: Corinna Vinschen <xda@vinschen.de>