Base64: Update documentation of decoding function
* The conversion only happens if
*
* - the value of the key has type `string`
- * - the key value starts with `ELEKTRA_PLUGIN_BASE64_PREFIX` (`@`).
+ * - the key value starts with `ELEKTRA_PLUGIN_BASE64_PREFIX` (`"@BASE64"`).
*
* .
*
* @retval -1 if the function was unable to convert the value of `key`
* @retval 0 if no conversion has taken place
- * @retval 1 if the function successfully converted the value of `key`
+ * @retval 1 if the function successfully converted the value of `key` or if the key value was not base64 encoded
*/
static int decode (Key * key, Key * parent)
{
