Check for HAVE_ISATTY.

Patch by Martin Storsjö <martin at martin dot st>

Originally committed as revision 19505 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -3968,8 +3968,10 @@ int main(int argc, char **argv)
     avdevice_register_all();
     av_register_all();
 
+#if HAVE_ISATTY
     if(isatty(STDIN_FILENO))
         url_set_interrupt_cb(decode_interrupt_cb);
+#endif
 
     for(i=0; i<CODEC_TYPE_NB; i++){
         avcodec_opts[i]= avcodec_alloc_context2(i);