Print "NOPTS" when AV_NOPTS_VALUE is encountered during seek regression tests.

This makes the output nicely aligned even in for those cases, and might
also avoid some issues with printf implementations that can not handle well
very large float values (e.g. msvcrt without MinGW wrapper IIRC).

Originally committed as revision 20334 to svn://svn.ffmpeg.org/ffmpeg/trunk