Assertion on current 6.2.x branch

#0  0x00002aaaad6bc37d in __libc_waitpid (pid=<optimized out>, stat_loc=<optimized out>, options=<optimized out>) at ../sysdeps/unix/sysv/linux/waitpid.c:41
#1  0x00002aaaaab81d37 in crash_logger_invoke (signo=6, info=0x2aaab440a330, ctx=0x2aaab440a200) at Crash.cc:164
#2  <signal handler called>
#3  0x00002aaaae807625 in *__GI_raise (sig=<optimized out>) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#4  0x00002aaaae808e05 in *__GI_abort () at abort.c:92
#5  0x00002aaaab996060 in ink_abort (message_format=message_format@entry=0x2aaaab9a302f "%s:%d: failed assertion `%s`") at ink_error.cc:79
#6  0x00002aaaab994165 in _ink_assert (expression=<optimized out>, file=<optimized out>, line=<optimized out>) at ink_assert.cc:37
#7  0x00002aaaaabcb8d0 in ProxyClientSession::state_api_callout (this=0x2aaabe730000, event=<optimized out>) at ProxyClientSession.cc:147
#8  0x00002aaaaacf0883 in Continuation::handleEvent (data=0x2aab37097938, event=100, this=0x2aaabe730000) at ../../iocore/eventsystem/I_Continuation.h:153
#9  Http2ClientSession::state_complete_frame_read (this=0x2aaabe730000, event=<optimized out>, edata=0x2aab37097938) at Http2ClientSession.cc:480
#10 0x00002aaaaacef082 in Http2ClientSession::main_event_handler (this=0x2aaabe730000, event=100, edata=0x2aab37097938) at Http2ClientSession.cc:294
#11 0x00002aaaaacf10a2 in Continuation::handleEvent (data=0x2aab37097938, event=100, this=0x2aaabe730000) at ../../iocore/eventsystem/I_Continuation.h:153
#12 Http2ClientSession::state_start_frame_read (this=0x2aaabe730000, event=<optimized out>, edata=0x2aab37097938) at Http2ClientSession.cc:448
#13 0x00002aaaaacef082 in Http2ClientSession::main_event_handler (this=0x2aaabe730000, event=100, edata=0x2aab37097938) at Http2ClientSession.cc:294
#14 0x00002aaaaae6868b in Continuation::handleEvent (data=0x2aab37097938, event=100, this=<optimized out>) at ../../iocore/eventsystem/I_Continuation.h:153
#15 read_signal_and_update (vc=0x2aab37097820, vc@entry=0x1, event=event@entry=100) at UnixNetVConnection.cc:148
#16 UnixNetVConnection::readSignalAndUpdate (this=this@entry=0x2aab37097820, event=event@entry=100) at UnixNetVConnection.cc:1030
#17 0x00002aaaaae47e43 in SSLNetVConnection::net_read_io (this=0x2aab37097820, nh=0x2aaab2d0acc0, lthread=0x2aaab2d07000) at SSLNetVConnection.cc:598
#18 0x00002aaaaae55d7c in NetHandler::mainNetEvent (this=0x2aaab2d0acc0, event=<optimized out>, e=<optimized out>) at UnixNet.cc:513
#19 0x00002aaaaae8db76 in Continuation::handleEvent (data=0x2aaab0bfa1c0, event=5, this=<optimized out>) at I_Continuation.h:153
#20 EThread::process_event (calling_code=5, e=0x2aaab0bfa1c0, this=0x2aaab2d07000) at UnixEThread.cc:148
#21 EThread::execute (this=0x2aaab2d07000) at UnixEThread.cc:275
#22 0x00002aaaaae8c976 in spawn_thread_internal (a=0x2aaab0b23d90) at Thread.cc:86
#23 0x00002aaaad6b4aa1 in start_thread (arg=0x2aaab440b700) at pthread_create.c:301
#24 0x00002aaaae8bd93d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115