cbs_h2645: Allocate all internal buffers with padding

Any of these buffers (for both H.264 and H.265) might reasonably be
parsed using the bitstream reader, so include padding on all of them.

libavcodec/cbs_h2645.c

@@ -319,7 +319,8 @@ static int cbs_h2645_read_more_rbsp_data(GetBitContext *gbc)
 #define byte_alignment(rw) (get_bits_count(rw) % 8)
 
 #define allocate(name, size) do { \
-        name ## _ref = av_buffer_allocz(size); \
+        name ## _ref = av_buffer_allocz(size + \
+                                        AV_INPUT_BUFFER_PADDING_SIZE); \
         if (!name ## _ref) \
             return AVERROR(ENOMEM); \
         name = name ## _ref->data; \