avformat/tty: Check avio_size()

Fixes: CID1220824 Overflowed constant

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/tty.c

@@ -123,7 +123,9 @@ static int read_header(AVFormatContext *avctx)
     s->chars_per_frame = FFMAX(av_q2d(st->time_base)*s->chars_per_frame, 1);
 
     if (avctx->pb->seekable & AVIO_SEEKABLE_NORMAL) {
-        s->fsize = avio_size(avctx->pb);
+        int64_t fsize = avio_size(avctx->pb);
+        if (fsize > 0) {
+            s->fsize = fsize;
             st->duration = (s->fsize + s->chars_per_frame - 1) / s->chars_per_frame;
 
             if (ff_sauce_read(avctx, &s->fsize, 0, 0) < 0)
@@ -131,6 +133,7 @@ static int read_header(AVFormatContext *avctx)
 
             avio_seek(avctx->pb, 0, SEEK_SET);
         }
+    }
 
 fail:
     return ret;