+/*
+ * Finds and returns the _first_ descriptor having the short option name
+ * `short_name` or the long option name `long_name` within the option
+ * descriptors `descrs`.
+ *
+ * `short_name` may be `'\0'` to not consider it.
+ *
+ * `long_name` may be `NULL` to not consider it.
+ *
+ * Returns `NULL` if no descriptor is found.
+ */