Do not enable simple_motion_search_prune_rect

av2_simple_motion_search_prune_rect() is not implemented for the AV2
partition set and asserts "Not implemented" since e2d0566. With
--disable-ml-partition-speed-features=0 the speed feature turned on, the
assert was compiled out under NDEBUG, and the encoder segfaulted:
av2_prune_partitions_before_search() calls the function for rectangular
block sizes, where convert_bsize_to_idx() returns -1 and sms_tree is NULL
because fill_sms_buf() only populates square sizes.

Default configurations are bit-identical; the speed feature was already
forced off there by av2_disable_ml_based_partition_sf().

Author: Xin Zhao

av2/encoder/speed_features.c

@@ -296,7 +296,16 @@ static void set_good_speed_features_framesize_independent(
   sf->gm_sf.disable_gm_search_based_on_stats = 1;
 
   sf->part_sf.less_rectangular_check_level = 1;
-  sf->part_sf.simple_motion_search_prune_rect = 1;
+  // Keep simple_motion_search_prune_rect off:
+  // av2_simple_motion_search_prune_rect() is not implemented for the AV2
+  // partition set (see the assert at the top of that function) and faults if
+  // reached. av2_prune_partitions_before_search() calls it for rectangular
+  // block sizes too, where convert_bsize_to_idx() returns -1 and sms_tree is
+  // NULL, since fill_sms_buf() only populates square sizes. Previously this was
+  // only unreachable because disable_ml_partition_speed_features defaults to 1;
+  // with --disable-ml-partition-speed-features=0 the encoder segfaulted. Do not
+  // set this to 1 without reimplementing the model for AV2.
+  sf->part_sf.simple_motion_search_prune_rect = 0;
 
   sf->inter_sf.disable_wedge_search_var_thresh = 0;
   // TODO(debargha): Test, tweak and turn on either 1 or 2