[BUG] Possible crash while sending crypto keys.

[maxsharabayko]

A crash in Travis CI was observed once in #2548. The PR itself does not look related to the issue.
There may be a chance it is related to #2541.

[ RUN      ] TestEnforcedEncryption.CASE_D_4_NonBlocking_Enforced_Off_Off_Pwd_None_Set
09:05:31.484224/SRT:RcvQ:w75!W:SRT.cn: @254575997: HS EXT: Agent declares encryption, but Peer does not (Agent can still receive unencrypted packets from Peer).
09:05:31.485487/SRT:RcvQ:w75!W:SRT.cn: @254575997: createSrtHandshake: Agent has PW, but Peer sent no KMREQ. Sending error KMRSP response
Epoll wait result: 1 FOUND: @254575998 in [R]
09:05:31.485936/SRT:RcvQ:w76!W:SRT.cn: @254575999: HS KMREQ: Peer declares encryption, but agent does not - still allowing connection.
09:05:31.485958/SRT:RcvQ:w76!W:SRT.cn: processSrtMsg_KMRSP: received failure report. STATE: NOSECRET
ACCEPT: done, result=254575997
[T] ACCEPT SUCCEEDED: @254575997
/home/travis/.travis/functions: line 109:  7067 Segmentation fault      ./test-srt --gtest_filter="-$TESTS_IPv6"

[maxsharabayko]

Also observed in #2546, Travis, Linux Debug.

TestEnforcedEncryption.CASE_C_1_NonBlocking_Enforced_Off_On_Pwd_Set_Set_Match
Epoll wait result: 1 FOUND: @359828802 in [R]
ACCEPT: done, result=359828801
[T] ACCEPT SUCCEEDED: @359828801
/home/travis/.travis/functions: line 109:  6985 Segmentation fault      ./test-srt --gtest_filter="-$TESTS_IPv6"

[maxsharabayko]

Also observed in #2433 on Travis, Linux Debug.2.

Debug BUILD_OPTS='-DENABLE_LOGGING=OFF -DUSE_ENCLIB=mbedtls -DENABLE_MONOTONIC_CLOCK=ON -DENABLE_BONDING=ON -DCMAKE_CXX_FLAGS="-Werror"'

ReuseAddr.SameAddr2
Bind to: 10.30.0.15:5000
Connecting to: 10.30.0.15:5000
Accepted from: 10.30.0.15:36927
Client exit
Server exit
Bind to: 10.30.0.15:5000
Connecting to: 10.30.0.15:5000
Accepted from: 10.30.0.15:55347
Client exit
Server exit
/home/travis/.travis/functions: line 109:  6975 Segmentation fault      ./test-srt --gtest_filter="-$TESTS_IPv6"

[maxsharabayko]

Master ef17a24, Travis Linux Debug.2.

[ RUN      ] TestEnforcedEncryption.CASE_A_1_Blocking_Enforced_On_On_Pwd_Set_Set_Match
ACCEPT: done, result=560786322
[T] ACCEPT SUCCEEDED: @560786322
/home/travis/.travis/functions: line 109:  6415 Segmentation fault      (core dumped) ./test-srt --gtest_filter="-$TESTS_IPv6"
[New LWP 6432]
[New LWP 6415]
[New LWP 6430]
[New LWP 6435]
[New LWP 6431]
[New LWP 6434]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./test-srt --gtest_filter=-TestMuxer.IPv4_and_IPv6:TestIPv6.v6_calls_v6*:ReuseA'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f5d2d63bd44 in pthread_mutex_lock () from /lib/x86_64-linux-gnu/libpthread.so.0
[Current thread is 1 (Thread 0x7f5d2b76f700 (LWP 6432))]
#0  0x00007f5d2d63bd44 in pthread_mutex_lock () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00000000008acd38 in srt::sync::Mutex::lock (this=0x98) at /home/travis/build/Haivision/srt/srtcore/sync_posix.cpp:220
#2  0x00000000008acd9e in srt::sync::ScopedLock::ScopedLock (this=0x7f5d2b76ec50, m=...) at /home/travis/build/Haivision/srt/srtcore/sync_posix.cpp:236
#3  0x0000000000851f86 in srt::CCryptoControl::sendKeysToPeer (this=0x0, sock=0x7f5d20000978, iSRTT=100000) at /home/travis/build/Haivision/srt/srtcore/crypto.cpp:452
#4  0x0000000000832cfb in srt::CUDT::checkSndTimers (this=0x7f5d20000978) at /home/travis/build/Haivision/srt/srtcore/core.cpp:5894
#5  0x0000000000840e6e in srt::CUDT::checkRexmitTimer (this=0x7f5d20000978, currtime=...) at /home/travis/build/Haivision/srt/srtcore/core.cpp:11184
#6  0x0000000000841258 in srt::CUDT::checkTimers (this=0x7f5d20000978) at /home/travis/build/Haivision/srt/srtcore/core.cpp:11281
#7  0x000000000087d026 in srt::CRcvQueue::worker_ProcessAddressedPacket (this=0x14c5680, id=560786322, unit=0x14d1db8, addr=...) at /home/travis/build/Haivision/srt/srtcore/queue.cpp:1444
#8  0x000000000087c962 in srt::CRcvQueue::worker (param=0x14c5680) at /home/travis/build/Haivision/srt/srtcore/queue.cpp:1219
#9  0x00007f5d2d6396ba in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#10 0x00007f5d2c87951d in clone () from /lib/x86_64-linux-gnu/libc.so.6
  Id   Target Id         Frame 
* 1    Thread 0x7f5d2b76f700 (LWP 6432) 0x00007f5d2d63bd44 in pthread_mutex_lock () from /lib/x86_64-linux-gnu/libpthread.so.0
  2    Thread 0x7f5d2da5e740 (LWP 6415) 0x00007f5d2d63a98d in pthread_join () from /lib/x86_64-linux-gnu/libpthread.so.0
  3    Thread 0x7f5d2c771700 (LWP 6430) 0x00007f5d2c83e38d in nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
  4    Thread 0x7f5d29f6c700 (LWP 6435) 0x00007f5d2d64294d in recvmsg () from /lib/x86_64-linux-gnu/libpthread.so.0
  5    Thread 0x7f5d2bf70700 (LWP 6431) 0x00007f5d2d63f360 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0
  6    Thread 0x7f5d2af6e700 (LWP 6434) 0x00007f5d2d63f360 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib/x86_64-linux-gnu/libpthread.so.0