avformat/westwood_vqa: Check ffio_ensure_seekback()

Fixes Coverity issue #1598405.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/westwood_vqa.c

@@ -201,8 +201,10 @@ static int wsvqa_read_packet(AVFormatContext *s,
             /* We need a big seekback buffer because there can be SNxx, VIEW and ZBUF
              * chunks (<512 KiB total) in the stream before we read VQFR (<256 KiB) and
              * seek back here. */
-            ffio_ensure_seekback(pb, wsvqa->vqfl_chunk_size + (512 + 256) * 1024);
+            ret = ffio_ensure_seekback(pb, wsvqa->vqfl_chunk_size + (512 + 256) * 1024);
             avio_skip(pb, chunk_size + skip_byte);
+            if (ret < 0)
+                return ret;
             continue;
         } else if ((chunk_type == SND0_TAG) || (chunk_type == SND1_TAG) ||
             (chunk_type == SND2_TAG) || (chunk_type == VQFR_TAG)) {