Only checks for jack if it is enabled and hence only links to jack if

it is not disabled.

Patch by Adrian Stutz $firsname@sttz ch.

Originally committed as revision 19277 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2215,7 +2215,7 @@ check_header soundcard.h
 
 check_lib2 alsa/asoundlib.h snd_pcm_htimestamp -lasound
 
-check_lib2 jack/jack.h jack_client_open -ljack
+enabled jack_demuxer && check_lib2 jack/jack.h jack_client_open -ljack
 
 # deal with the X11 frame grabber
 enabled x11grab                         &&