Increase min size of compressed data

This commit increases the minimum size for allocated buffer for
compressed data. The old size underestimated the size needed for
small images with width or height less than 64 pixels.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=31

Change-Id: Ia12507edc2be1e737ec49c32f64fd2ebf1eab41f

av1/av1_cx_iface.c

@@ -932,6 +932,7 @@ static aom_codec_frame_flags_t get_frame_pkt_flags(const AV1_COMP *cpi,
   return flags;
 }
 
+const size_t kMinCompressedSize = 8192;
 static aom_codec_err_t encoder_encode(aom_codec_alg_priv_t *ctx,
                                       const aom_image_t *img,
                                       aom_codec_pts_t pts,
@@ -959,7 +960,7 @@ static aom_codec_err_t encoder_encode(aom_codec_alg_priv_t *ctx,
       data_sz = ctx->cfg.g_w * ctx->cfg.g_h * get_image_bps(img) / 8 *
                 (cpi->multi_arf_allowed ? 8 : 2);
 #endif  // CONFIG_EXT_REFS
-      if (data_sz < 4096) data_sz = 4096;
+      if (data_sz < kMinCompressedSize) data_sz = kMinCompressedSize;
       if (ctx->cx_data == NULL || ctx->cx_data_sz < data_sz) {
         ctx->cx_data_sz = data_sz;
         free(ctx->cx_data);