A bug that can lead freemodbus server to crash

[CAPCOMIN]

Hi,
I found this bug which leads demo/LINUXTCP to crash while conducting fuzzing experiment.

The log information of message which lead server to crash:
modbusbug2.txt

The ASAN information:

=================================================================
==9863==ERROR: AddressSanitizer: SEGV on unknown address 0x000009026928 (pc 0x0000004c4c97 bp 0x7f2c32efede0 sp 0x7f2c32efed20 T1)
==9863==The signal is caused by a READ memory access.
    #0 0x4c4c97 in xMBPortTCPPool /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/port/porttcp.c:205:13
    #1 0x4c4667 in xMBPortEventGet /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/port/portevent.c:69:17
    #2 0x4c6084 in eMBPoll /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/../../modbus/mb.c:351:9
    #3 0x4c416f in pvPollingThread /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/demo.c:215:17
    #4 0x7f2c36853608 in start_thread (/lib/x86_64-linux-gnu/libpthread.so.0+0x8608)
    #5 0x7f2c365fe352 in clone (/lib/x86_64-linux-gnu/libc.so.6+0x11f352)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/port/porttcp.c:205:13 in xMBPortTCPPool
Thread T1 created by T0 here:
    #0 0x47e85a in pthread_create (/home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/tcpmodbus+0x47e85a)
    #1 0x4c39db in bCreatePollingThread /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/demo.c:189:13
    #2 0x4c3502 in main /home/linuxbrew/pin-3.28-98749-g6643ecee5-gcc-linux/source/tools/BinPRE/src/freemodbus/demo/LINUXTCP/demo.c:126:21
    #3 0x7f2c36503082 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24082)

==9863==ABORTING