Failure in 4.2.5 when zmq_poller_destroy is called after zmq_ctx_term

[sigiesec]

Issue description

When you have a poller, which is terminated because the zmq context was terminated, you still need to destroy it with zmq_poller_destroy. This causes an assertion.

IIRC, this worked fine in 4.2.3

Environment

• libzmq version (commit hash if unreleased): 4.2.5
• OS: Windows 7 64-bit

Minimal test code / Steps to reproduce the issue

See test case in sigiesec@b047e91#diff-1c46bf5e98b1e63ffd182e7078863236

What's the actual result? (include assertion message & call stack if applicable)

Assertion failed: rc == 0 (d:\nls\libzmq\src\socket_poller.cpp:41)

What's the expected result?

Executes without failure.