[NORMATIVE-DECODING, intra-edge] Fix bug in is_smooth()

Because the mbmi pointer passed into is_smooth comes from the above/left
block, it might be an inter block. If this happens, we correctly deduce
that the above/left block does not use a smooth intra mode.

However, inter blocks do not set mbmi->uv_mode, so in the UV case we end up
reading stale data. This may result in is_smooth() returning the wrong value,
if (whatever was previously written into) mbmi->uv_mode happens to be a
smooth intra mode.

Fix this by including an explicit check for inter blocks.

BUG=aomedia:1362

Change-Id: I3ec9faef9b6297e22915176067b5704003bc4664

av1/common/reconintra.c

diff --git a/av1/common/reconintra.c b/av1/common/reconintra.c
index 5e1b5de..b9d266f 100644
--- a/av1/common/reconintra.c
+++ b/av1/common/reconintra.c
@@ -1398,6 +1398,10 @@
     return (mode == SMOOTH_PRED || mode == SMOOTH_V_PRED ||
             mode == SMOOTH_H_PRED);
   } else {
+    // uv_mode is not set for inter blocks, so need to explicitly
+    // detect that case.
+    if (is_inter_block(mbmi)) return 0;
+
     const UV_PREDICTION_MODE uv_mode = mbmi->uv_mode;
     return (uv_mode == UV_SMOOTH_PRED || uv_mode == UV_SMOOTH_V_PRED ||
             uv_mode == UV_SMOOTH_H_PRED);