huffyuv: add padding to classic (v1) huffman tables.

We slightly overread the input buffer, so we require
padding at the end of the buffer, as is documented in the
get_bits API. Without padding, we'll read uninitialized
data or beyond the end of the .rodata, which may crash.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/huffyuv.c

@@ -82,13 +82,15 @@ typedef struct HYuvContext{
     DSPContext dsp;
 }HYuvContext;
 
-static const unsigned char classic_shift_luma[] = {
+#define classic_shift_luma_table_size 42
+static const unsigned char classic_shift_luma[classic_shift_luma_table_size + FF_INPUT_BUFFER_PADDING_SIZE] = {
   34,36,35,69,135,232,9,16,10,24,11,23,12,16,13,10,14,8,15,8,
   16,8,17,20,16,10,207,206,205,236,11,8,10,21,9,23,8,8,199,70,
   69,68, 0
 };
 
-static const unsigned char classic_shift_chroma[] = {
+#define classic_shift_chroma_table_size 59
+static const unsigned char classic_shift_chroma[classic_shift_chroma_table_size + FF_INPUT_BUFFER_PADDING_SIZE] = {
   66,36,37,38,39,40,41,75,76,77,110,239,144,81,82,83,84,85,118,183,
   56,57,88,89,56,89,154,57,58,57,26,141,57,56,58,57,58,57,184,119,
   214,245,116,83,82,49,80,79,78,77,44,75,41,40,39,38,37,36,34, 0
@@ -366,10 +368,10 @@ static int read_old_huffman_tables(HYuvContext *s){
     GetBitContext gb;
     int i;
 
-    init_get_bits(&gb, classic_shift_luma, sizeof(classic_shift_luma)*8);
+    init_get_bits(&gb, classic_shift_luma, classic_shift_luma_table_size*8);
     if(read_len_table(s->len[0], &gb)<0)
         return -1;
-    init_get_bits(&gb, classic_shift_chroma, sizeof(classic_shift_chroma)*8);
+    init_get_bits(&gb, classic_shift_chroma, classic_shift_chroma_table_size*8);
     if(read_len_table(s->len[1], &gb)<0)
         return -1;