Fix coverity CID #1454815 - NULL ptr dereference in initthread.c

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/12708)

crypto/initthread.c

@@ -392,13 +392,14 @@ static int init_thread_deregister(void *index, int all)
     for (i = 0; i < sk_THREAD_EVENT_HANDLER_PTR_num(gtr->skhands); i++) {
         THREAD_EVENT_HANDLER **hands
             = sk_THREAD_EVENT_HANDLER_PTR_value(gtr->skhands, i);
-        THREAD_EVENT_HANDLER *curr = *hands, *prev = NULL, *tmp;
+        THREAD_EVENT_HANDLER *curr = NULL, *prev = NULL, *tmp;
 
         if (hands == NULL) {
             if (!all)
                 CRYPTO_THREAD_unlock(gtr->lock);
             return 0;
         }
+        curr = *hands;
         while (curr != NULL) {
             if (all || curr->index == index) {
                 if (prev != NULL)