init_get_bits8: zero pointers & struct on error

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/get_bits.h

@@ -407,7 +407,7 @@ static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
                                  int byte_size)
 {
     if (byte_size > INT_MAX / 8 || byte_size < 0)
-        return AVERROR_INVALIDDATA;
+        byte_size = -1;
     return init_get_bits(s, buffer, byte_size * 8);
 }