kvs: preserve errno in kvs_wait_version_destroy()

Problem: The internal function kvs_wait_version_destroy() does not
preserve errno when it is called.

Preserve errno when kvs_wait_version_destroy() is called.

Author: chu11

src/modules/kvs/kvs_wait_version.c

@@ -50,8 +50,10 @@ static void kvs_wait_version_destroy (void *data)
 {
     struct kvs_wait_version *ks = data;
     if (ks) {
+        int save_errno = errno;
         flux_msg_decref (ks->msg);
         free (ks);
+        errno = save_errno;
     }
 }