free NULL cleanup

This commit handles BIO_ACCEPT_free BIO_CB_FREE BIO_CONNECT_free
BIO_free BIO_free_all BIO_vfree

Reviewed-by: Matt Caswell <matt@openssl.org>
diff --git a/demos/bio/server-arg.c b/demos/bio/server-arg.c
index 7ba54db..4f65227 100644
--- a/demos/bio/server-arg.c
+++ b/demos/bio/server-arg.c
@@ -137,8 +137,7 @@
     if (ret) {
         ERR_print_errors_fp(stderr);
     }
-    if (in != NULL)
-        BIO_free(in);
+    BIO_free(in);
     exit(ret);
     return (!ret);
 }