Enable generic index creation and seeking for NUV demuxer.

Originally committed as revision 17966 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/nuv.c

@@ -259,4 +259,5 @@ AVInputFormat nuv_demuxer = {
     nuv_packet,
     NULL,
     NULL,
+    .flags = AVFMT_GENERIC_INDEX,
 };