Fix an uninitialized mv for sms at top-left of the tile

BUG=aomedia:3093

STATS_CHANGED

Change-Id: I494c62e5ad86279e48a65932da9927bd7d207b5d

av1/encoder/partition_strategy.c

diff --git a/av1/encoder/partition_strategy.c b/av1/encoder/partition_strategy.c
index a319175..8b9ac1d 100644
--- a/av1/encoder/partition_strategy.c
+++ b/av1/encoder/partition_strategy.c
@@ -2371,8 +2371,13 @@
   av1_find_mv_refs(cm, xd, xd->mi[0], ref_frame, mbmi_ext.ref_mv_count,
                    xd->ref_mv_stack, xd->weight, NULL, mbmi_ext.global_mvs,
                    mbmi_ext.mode_context);
-  ref_mvs[ref_frame] =
-      get_fullmv_from_mv(&xd->ref_mv_stack[ref_frame][0].this_mv.as_mv);
+  if (mbmi_ext.ref_mv_count[ref_frame] > 0) {
+    ref_mvs[ref_frame] =
+        get_fullmv_from_mv(&xd->ref_mv_stack[ref_frame][0].this_mv.as_mv);
+  } else {
+    ref_mvs[ref_frame] =
+        get_fullmv_from_mv(&mbmi_ext.global_mvs[ref_frame].as_mv);
+  }
 
   init_simple_motion_search_mvs(sms_root, ref_mvs);
 }