config_target_level: fix crash w/CONFIG_REALTIME_ONLY=1

`twopass->stats_buf_ctx` is `NULL` when this configuration is set. The
initialization is skipped in `encoder_init()`.

Change-Id: Ic74388e721912766db598649e1739992e0373a58

av1/encoder/rc_utils.h

diff --git a/av1/encoder/rc_utils.h b/av1/encoder/rc_utils.h
index 82ab1b2..1a5949f 100644
--- a/av1/encoder/rc_utils.h
+++ b/av1/encoder/rc_utils.h
@@ -74,12 +74,14 @@
       av1_get_max_bitrate_for_level(target_level, tier, profile);
   const int64_t max_bitrate = (int64_t)(level_bitrate_limit * 0.70);
   rc_cfg->target_bandwidth = AOMMIN(rc_cfg->target_bandwidth, max_bitrate);
+#if !CONFIG_REALTIME_ONLY
   // Also need to update cpi->ppi->twopass.bits_left.
   TWO_PASS *const twopass = &cpi->ppi->twopass;
   FIRSTPASS_STATS *stats = twopass->stats_buf_ctx->total_stats;
   if (stats != NULL)
     cpi->ppi->twopass.bits_left =
         (int64_t)(stats->duration * rc_cfg->target_bandwidth / 10000000.0);
+#endif
 
   // Adjust max over-shoot percentage.
   rc_cfg->over_shoot_pct = 0;