Windows - ipc_send_cb crash

[mikisch81]

Describe the bug
Crash in ipc_send_cb in stressed reqrep example

Expected behavior
Client and server run without any crash

Actual Behavior
At one point client calls nng_send and a crash happens in the invocation of ipc_send_cb.

To Reproduce
Run the modified version of the reqrep example with ipc transport from here: https://gist.github.com/mikisch81/428c4ad87afcc1c8881b282cd5e80eb3

This example also was used to reproduce #1827 and #1837

Server: reqrep.exe server ipc://testing.nng
Client: reqrep.exe client ipc://testing.nng

** Environment Details **

• NNG version: 1.9.0
• Operating system and version: Windows 10
• Compiler and language used: C/C++ clang
• Shared or static library: static

Additional context