avcodec/mpeg12dec: Fix integer overflow

Fixes: signal_sigabrt_7ffff6ac8cc9_686_cov_1897408623_microsoft_new_way_to_shove_mpeg2_in_asf.dvr_ms

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpeg12dec.c

@@ -1490,7 +1490,7 @@ static void mpeg_decode_sequence_extension(Mpeg1Context *s1)
     s->width  |= (horiz_size_ext << 12);
     s->height |= (vert_size_ext  << 12);
     bit_rate_ext = get_bits(&s->gb, 12);  /* XXX: handle it */
-    s->bit_rate += (bit_rate_ext << 18) * 400;
+    s->bit_rate += (bit_rate_ext << 18) * 400LL;
     check_marker(&s->gb, "after bit rate extension");
     s->avctx->rc_buffer_size += get_bits(&s->gb, 8) * 1024 * 16 << 10;
 
@@ -2175,7 +2175,7 @@ static int mpeg1_decode_sequence(AVCodecContext *avctx,
                "frame_rate_index %d is invalid\n", s->frame_rate_index);
         s->frame_rate_index = 1;
     }
-    s->bit_rate = get_bits(&s->gb, 18) * 400;
+    s->bit_rate = get_bits(&s->gb, 18) * 400LL;
     if (check_marker(&s->gb, "in sequence header") == 0) {
         return AVERROR_INVALIDDATA;
     }