sysInfo: Check BarringInfoList presence before unpacking

[Jojeker]

Otherwise, the UE crashes with a NULL Derference. This patch should introduce the check before accessing the barring bits.

From the specification 3GPP TS 38.331 the uac-BarringInfo is defined as optional:

uac-BarringInfo SEQUENCE {
      uac-BarringForCommon [UAC-BarringPerCatList] OPTIONAL, -- Need S
      uac-BarringPerPLMN-List [UAC-BarringPerPLMN-List] OPTIONAL, -- Need S
      uac-BarringInfoSetList [UAC-BarringInfoSetList],
      uac-AccessCategory1-SelectionAssistanceInfo CHOICE {
         plmnCommon [UAC-AccessCategory1-SelectionAssistanceInfo],
         individualPLMNList SEQUENCE (SIZE (2..[maxPLMN]) OF [UAC-AccessCategory1-SelectionAssistanceInfo]
         } OPTIONAL-- Need S
      } OPTIONAL, -- Need R

Cheers,
Eduard