src/notify.c: Fix printf() misuse

Make sure we actually copy the notification warning interval to the
correct buffer instead of printing it to stdout (using an arbitrary
format string). This makes sure the current warning interval is shown
when editing the field and also eliminates a potential format string
vulnerability.

Spotted with "-Wformat-nonliteral".

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/notify.c

@@ -777,7 +777,7 @@ notify_config_bar (void)
         case '4':
           status_mesg (count_str, "");
           pthread_mutex_lock (&nbar.mutex);
-          printf (buf, "%d", nbar.cntdwn);
+          snprintf (buf, BUFSIZ, "%d", nbar.cntdwn);
           pthread_mutex_unlock (&nbar.mutex);
           if (updatestring (win[STA].p, &buf, 0, 1) == 0 &&
               is_all_digit (buf) && atoi (buf) >= 0 && atoi (buf) <= DAYINSEC)