Coverity fix in apps/oscp

CID 1440002 (#1 of 1): Use after free (USE_AFTER_FREE)
Not a deadly error, because error was just before app exit.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7359)

(cherry picked from commit 39fc4c17c4)

apps/ocsp.c

@@ -863,6 +863,7 @@ static void killall(int ret, pid_t *kidpids)
     for (i = 0; i < multi; ++i)
         if (kidpids[i] != 0)
             (void)kill(kidpids[i], SIGTERM);
+    OPENSSL_free(kidpids);
     sleep(1);
     exit(ret);
 }
@@ -977,7 +978,6 @@ static void spawn_loop(void)
     }
 
     /* The loop above can only break on termsig */
-    OPENSSL_free(kidpids);
     syslog(LOG_INFO, "terminating on signal: %d", termsig);
     killall(0, kidpids);
 }