ffmpeg: dont call exit_program() from a signal hander

This is unsafe and can deadlock amongth other things
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -328,7 +328,7 @@ sigterm_handler(int sig)
     received_nb_signals++;
     term_exit_sigsafe();
     if(received_nb_signals > 3)
-        exit_program(123);
+        exit(123);
 }
 
 void term_init(void)