Fix zero-length gnu_printf format string warning.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -444,7 +444,7 @@ static int configure_video_filters(AVInputStream *ist, AVOutputStream *ost)
 
 static void term_exit(void)
 {
-    av_log(NULL, AV_LOG_QUIET, "");
+    av_log(NULL, AV_LOG_QUIET, "%s", "");
 #if HAVE_TERMIOS_H
     if(!run_as_daemon)
         tcsetattr (0, TCSANOW, &oldtty);

ffplay.c

@@ -904,7 +904,7 @@ static void do_exit(void)
     if (show_status)
         printf("\n");
     SDL_Quit();
-    av_log(NULL, AV_LOG_QUIET, "");
+    av_log(NULL, AV_LOG_QUIET, "%s", "");
     exit(0);
 }
 

libavutil/log.h

@@ -159,7 +159,7 @@ const char* av_default_item_name(void* ctx);
  * "Last message repeated x times" messages below (f)printf messages with some
  * bad luck.
  * Also to receive the last, "last repeated" line if any, the user app must
- * call av_log(NULL, AV_LOG_QUIET, ""); at the end
+ * call av_log(NULL, AV_LOG_QUIET, "%s", ""); at the end
  */
 #define AV_LOG_SKIP_REPEATED 1
 void av_log_set_flags(int arg);