Inaccurate license detection for SPDX license identifier with trimmed, missing trailing parens

A text exactly as `SPDX-License-Identifier: (GPL-2.0-or-later WITH Bootloader-exception` (with a missing trailing paren) will be detected as `(gpl-2.0-plus AND bootloader-exception) AND unknown-spdx` where `unknown-spdx` comes from the missing trailing paren making the expression invalid from strict validation perspective.
We should allow and cope with these kind of cases which can be characterized as the presence of a single opening paren.