asf: Check return value of more avio_seek calls

This reduces problems when underlying protocol is not
seekable even if marked as such or if the file has been
cut short.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/asfdec.c

@@ -1155,7 +1155,8 @@ static int64_t asf_read_pts(AVFormatContext *s, int stream_index, int64_t *ppos,
     if (s->packet_size > 0)
         pos= (pos+s->packet_size-1-s->data_offset)/s->packet_size*s->packet_size+ s->data_offset;
     *ppos= pos;
-    avio_seek(s->pb, pos, SEEK_SET);
+    if (avio_seek(s->pb, pos, SEEK_SET) < 0)
+        return AV_NOPTS_VALUE;
 
 //printf("asf_read_pts\n");
     asf_reset_header(s);
@@ -1197,7 +1198,9 @@ static void asf_build_simple_index(AVFormatContext *s, int stream_index)
     int64_t current_pos= avio_tell(s->pb);
     int i;
 
-    avio_seek(s->pb, asf->data_object_offset + asf->data_object_size, SEEK_SET);
+    if(avio_seek(s->pb, asf->data_object_offset + asf->data_object_size, SEEK_SET) < 0)
+        return;
+
     ff_get_guid(s->pb, &g);
 
     /* the data object can be followed by other top-level objects,
@@ -1269,7 +1272,8 @@ static int asf_read_seek(AVFormatContext *s, int stream_index, int64_t pts, int
 
             /* do the seek */
             av_log(s, AV_LOG_DEBUG, "SEEKTO: %"PRId64"\n", pos);
-            avio_seek(s->pb, pos, SEEK_SET);
+            if(avio_seek(s->pb, pos, SEEK_SET) < 0)
+                return -1;
             asf_reset_header(s);
             return 0;
         }