Cosmetics: add empty line which was previously removed.

Improve readability.

Originally committed as revision 25882 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -12,6 +12,7 @@ libavutil:   2009-03-08
 
 
 API changes, most recent first:
+
 2010-12-04 - r25879 - lavu 50.34.0 - av_get_pix_fmt_string()
   Deprecate avcodec_pix_fmt_string() in favor of
   pixdesc.h/av_get_pix_fmt_string().