res_rtp_asterisk.c: Fix memory leak in ephemeral certificate creation.

Fixes #386

res/res_rtp_asterisk.c

@@ -2029,9 +2029,12 @@ static int create_ephemeral_certificate(EVP_PKEY *keypair, X509 **certificate)
 	if (!(serial = BN_new())
 	   || !BN_rand(serial, SERIAL_RAND_BITS, -1, 0)
 	   || !BN_to_ASN1_INTEGER(serial, X509_get_serialNumber(cert))) {
+		BN_free(serial);
 		goto error;
 	}
 
+	BN_free(serial);
+
 	/*
 	 * Validity period - Current Chrome & Firefox make it 31 days starting
 	 * with yesterday at the current time, so we will do the same.
@@ -2066,7 +2069,6 @@ static int create_ephemeral_certificate(EVP_PKEY *keypair, X509 **certificate)
 	return 0;
 
 error:
-	BN_free(serial);
 	X509_free(cert);
 
 	return -1;