Fix --enable-ab-partitions=0

Make sure AB partitions are disabled when --enable-ab-partitions=0.

Change-Id: I8697f8e95a9d2306b4a3959ef379a765ec807ce7

av1/encoder/partition_strategy.c

diff --git a/av1/encoder/partition_strategy.c b/av1/encoder/partition_strategy.c
index 1c0f1bd..4b44ba4 100644
--- a/av1/encoder/partition_strategy.c
+++ b/av1/encoder/partition_strategy.c
@@ -1993,6 +1993,7 @@
   // Pruning: pruning out some ab partitions using a DNN taking rd costs of
   // sub-blocks from previous basic partition types.
   if (cpi->sf.part_sf.ml_prune_partition && ext_partition_allowed &&
+      part_cfg->enable_ab_partitions &&
       part_state->partition_rect_allowed[HORZ] &&
       part_state->partition_rect_allowed[VERT]) {
     // TODO(huisu@google.com): x->source_variance may not be the current