fixes #948 Handle leak on Windows

Thanks to @SEFIROT-GmbH for the fix.
diff --git a/src/core/sock.c b/src/core/sock.c
index da32930..8348d30 100644
--- a/src/core/sock.c
+++ b/src/core/sock.c
@@ -235,6 +235,7 @@
     nn_fsm_stopped_noevent (&self->fsm);
     nn_fsm_term (&self->fsm);
     nn_sem_term (&self->termsem);
+    nn_sem_term (&self->relesem);
     nn_list_term (&self->sdeps);
     nn_list_term (&self->eps);
     nn_ctx_term (&self->ctx);