undefined behavior in posix ipc_dialer_dial

[JoshSalitSonos]

Describe the bug
In the ipc_dialer_dial implementation in src/platform/posix/posix_ipcdial.c, if nni_posix_pfd_init fails then goto error is executed, and nni_mtx_unlock(&d->mtx) is called without the mutex having been locked. this passes through to a pthread_mutex_unlock call, which is documented as having undefined behavior if the mutex is not locked.

nng/src/platform/posix/posix_ipcdial.c

Lines 190 to 191 in c5e9d8a

	if ((rv = nni_posix_pfd_init(&pfd, fd)) != 0) {
	goto error;

It looks like this was introduced by PR #1111.

To Reproduce
This was found via code inspection.

** Environment Details **

• NNG version - commit c5e9d8a
• linux (various kernels)

[gdamore]

The TCP code path suffers the same flaw.

[gdamore]

One note for anyone looking at this -- short of running of out RAM, it's exceedingly unlikely that you've observed this particular bug. The failure path here should really not be one we expect to see executed.