net/ssl-bear: NULL-check calloc in ssl_socket_init

ssl_socket_init calloc'd its ssl_state struct but dereferenced it
immediately on the next line:

    struct ssl_state *state = (struct ssl_state*)calloc(1, sizeof(*state));
    initialize();
    br_ssl_client_init_full(&state->sc, &state->xc, TAs, TAs_NUM);

On OOM, &state->sc segfaults before the br_ssl_client_init_full
call can even begin.

Fix: NULL-check after calloc and return NULL on failure.  The
caller (net_http.c line 1030:

    if (!(conn->ssl_ctx = ssl_socket_init(conn->fd, ...)))
       ...

) already treats a NULL return as 'SSL setup failed, abort the
connection', so returning NULL on OOM integrates cleanly.

The sibling at net_socket_ssl_mbed.c:96 has the same bug and will
be addressed in a follow-up.

Thread-safety: unchanged.  ssl_socket_init is called once per
HTTPS connection from whichever thread is servicing that
connection's http_t state.

Author: LibretroAdmin

libretro-common/net/net_socket_ssl_bear.c

@@ -233,6 +233,13 @@ void* ssl_socket_init(int fd, const char *domain)
 {
    struct ssl_state *state = (struct ssl_state*)calloc(1, sizeof(*state));
 
+   /* NULL-check before any of the br_ssl_* calls below dereference
+    * state.  The pre-patch form segfaulted on OOM at the first
+    * br_ssl_client_init_full(&state->sc, ...) call.  Caller
+    * (net_http.c line 1030) already NULL-checks our return. */
+   if (!state)
+      return NULL;
+
    initialize();
 
    br_ssl_client_init_full(&state->sc, &state->xc, TAs, TAs_NUM);