Fixed Deriving and Getting the StreamID Socket Option on a Group

[maxsharabayko]

• Fix CUDTGroup::getOpt(..): check value length in group config storage. The storage could have empty strings, and dereferencing the first element must not happen.
• Fixed deriving string options by a group. SRTO_STREAMID, SRTO_PACKETFILTER are directly affected. SRTO_PASSPHRASE was derived correctly.
• Extended Bonding.Options unit test with Stream ID and linger set/get check.

Fixes #3072.

[maxsharabayko]

v1.5.4 Release Build on a local host. Note "Stream ID: not set" is reported by the receiver upon connection (srt_getsockopt fails to return a value, also std::vector out of range assertion will be triggered in a debug build).

(sender)
$> srt-xtransmit generate "srt://127.0.0.1:4200?grouptype=broadcast&streamid=abcdefg" --duration 1s --sendrate 100kbps
15:20:33.484373 [I] CONN Establishing connection no.1.
15:20:33.496851 [I] PACER sendrate 100000 bps (inter send interval 106382 us)
15:20:34.574192 [I] PIPE Pipe exit (conn @2093138386), 0 remain active.

(receiver)
$> srt-xtransmit receive srt://:4200?groupconnect=1
15:20:22.741243 [I] CONN Establishing connection no.1.
15:20:22.748278 [I] SOCKET::SRT srt://:4200: bound to ':4200'.
15:20:33.495838 [I] SOCKET::SRT @268705253 (srt://:4200) Accepted connection @1342447075. TSBPD Latency RCV 120ms, peer 0ms. KM state UNSECURED (RCV UNSECURED, SND UNSECURED). PB key length: 0. Cryptomode AUTO. Stream ID: not set.
15:20:34.872000/T87372*E:SRT.gr: grp/recv: $1342447075: ABANDONING: opened=false connected=false
15:20:34.872917 [W] RECEIVE read::recv: Connection does not exist
15:20:34.873611 [I] PIPE Pipe exit (conn @1342447075), 0 remain active.

With PR 3075 the Stream ID is correct (srt_getsockopt returns a correct value):

$> srt-xtransmit receive srt://:4200?groupconnect=1
15:33:02.551876 [I] CONN Establishing connection no.1.
15:33:02.556806 [I] SOCKET::SRT srt://:4200: bound to ':4200'.
15:33:03.495007 [I] SOCKET::SRT @700298265 (srt://:4200) Accepted connection @1774040087. TSBPD Latency RCV 120ms, peer 0ms. KM state UNSECURED (RCV UNSECURED, SND UNSECURED). PB key length: 0. Cryptomode AUTO. Stream ID: abcdefg.
15:33:04.579000/T71984*E:SRT.gr: grp/recv: $1774040087: ABANDONING: opened=false connected=false
15:33:04.580929 [W] RECEIVE read::recv: Connection does not exist
15:33:04.581270 [I] PIPE Pipe exit (conn @1774040087), 0 remain active.