Fix pem_passwd_cb(): unused variable "rwflag" (OpenSSL)

This patch fixes the following warning of GCC (version 4.3.2) in
function pem_passwd_cb() when compiling with OpenSSL support and
without debug code:

conn-ssl.c: In function 'pem_passwd_cb':
conn-ssl.c:122: warning: unused parameter 'rwflag'

src/ngircd/conn-ssl.c

@@ -123,7 +123,10 @@ pem_passwd_cb(char *buf, int size, int rwflag, void *password)
 {
 	array *pass = password;
 	int passlen;
-	assert(rwflag == 0); /* 0 -> callback used for decryption. See SSL_CTX_set_default_passwd_cb(3) */
+
+	(void)rwflag;		/* rwflag is unused if DEBUG is not set. */
+	assert(rwflag == 0);	/* 0 -> callback used for decryption.
+				 * See SSL_CTX_set_default_passwd_cb(3) */
 
 	passlen = (int) array_bytes(pass);