avcodec/ac3_parser: Check init_get_bits8() for failure

Fixes: CID1420393 Unchecked return value

Sponsored-by: Sovereign Tech Fund
Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 63415168db)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ac3_parser.c

@@ -204,7 +204,9 @@ int av_ac3_parse_header(const uint8_t *buf, size_t size,
     AC3HeaderInfo hdr;
     int err;
 
-    init_get_bits8(&gb, buf, size);
+    err = init_get_bits8(&gb, buf, size);
+    if (err < 0)
+        return AVERROR_INVALIDDATA;
     err = ff_ac3_parse_header(&gb, &hdr);
     if (err < 0)
         return AVERROR_INVALIDDATA;