Avoid placing fwd-kf when altref is not allowed

Change-Id: I3037244b830371c6fa3d0ebbcc12c4975b5711b2

av1/encoder/pass2_strategy.c

diff --git a/av1/encoder/pass2_strategy.c b/av1/encoder/pass2_strategy.c
index f9347fe..aa2a6f6 100644
--- a/av1/encoder/pass2_strategy.c
+++ b/av1/encoder/pass2_strategy.c
@@ -1137,7 +1137,7 @@
   // Set the interval until the next gf.
   // If forward keyframes are enabled, ensure the final gf group obeys the
   // MIN_FWD_KF_INTERVAL.
-  if (cpi->oxcf.fwd_kf_enabled &&
+  if (cpi->oxcf.fwd_kf_enabled && use_alt_ref &&
       ((twopass->stats_in - i + rc->frames_to_key) < twopass->stats_in_end)) {
     if (i == rc->frames_to_key) {
       rc->baseline_gf_interval = i;