Fix segmentation fault in decoder

Segmentation fault when decoding (caused by
"Implement on the fly padding in decoder") has
been fixed.

BUG=aomedia:1950

Change-Id: Iec2633ae4d6493abd1c76638ceedb49d27c206b1

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index a0645e8..c01c211 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -2752,7 +2752,7 @@
       aom_free(thread_data->mc_buf[ref]);
     thread_data->mc_buf[ref] = NULL;
   }
-  aom_free(thread_data->mc_buf);
+  thread_data->mc_buf_size = 0;
 }
 
 static void allocate_mc_tmp_buf(AV1_COMMON *const cm, void *td, int buf_size,

av1/decoder/decoder.h

diff --git a/av1/decoder/decoder.h b/av1/decoder/decoder.h
index 454456c..9da7ff3 100644
--- a/av1/decoder/decoder.h
+++ b/av1/decoder/decoder.h
@@ -40,7 +40,7 @@
   DECLARE_ALIGNED(32, tran_low_t, dqcoeff[MAX_TX_SQUARE]);
   DECLARE_ALIGNED(16, uint8_t, color_index_map[2][MAX_PALETTE_SQUARE]);
   uint8_t *mc_buf[2];
-  uint16_t mc_buf_size;
+  int32_t mc_buf_size;
 } ThreadData;
 
 typedef struct TileDataDec {