avformat/tta: fix crash with corrupted files

av_add_index_entry() can fail, for example because the parameters are
invalid, or because memory allocation fails. Check this; it can actually
happen with corrupted files.

The second hunk is just for robustness. Just in case functions like
ff_reduce_index() remove entries. (Not sure if this can actually
happen.)

Fixes ticket #4294.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/tta.c

@@ -118,8 +118,10 @@ static int tta_read_header(AVFormatContext *s)
     ffio_init_checksum(s->pb, tta_check_crc, UINT32_MAX);
     for (i = 0; i < c->totalframes; i++) {
         uint32_t size = avio_rl32(s->pb);
-        av_add_index_entry(st, framepos, i * c->frame_size, size, 0,
-                           AVINDEX_KEYFRAME);
+        int r;
+        if ((r = av_add_index_entry(st, framepos, i * c->frame_size, size, 0,
+                                    AVINDEX_KEYFRAME)) < 0)
+            return r;
         framepos += size;
     }
     crc = ffio_get_checksum(s->pb) ^ UINT32_MAX;
@@ -153,6 +155,11 @@ static int tta_read_packet(AVFormatContext *s, AVPacket *pkt)
     if (c->currentframe >= c->totalframes)
         return AVERROR_EOF;
 
+    if (st->nb_index_entries < c->totalframes) {
+        av_log(s, AV_LOG_ERROR, "Index entry disappeared\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     size = st->index_entries[c->currentframe].size;
 
     ret = av_get_packet(s->pb, pkt, size);