BUG: operator error - parenthetical without match fails silently

[elrayle]

Description

An open parenthesis in an expression should always have a matching close parenthesis. In the initial implementation in PR #1 , it was noted that a mismatch was silently ignored and swallowed at least the next following token. This leads to an invalid set of tokens instead of an error message.

Expected Behavior

When a matching close parenthesis is not in an expression, an error message should be returned from the scan function.

Proposed New Test

Add the following test (and perhaps other variations) to test for unmatched parentheses to the TestScan function in scan_test.go.

		{"operator error - malformed parenthetical", "(MIT",
		    []token{}, errors.New("open parenthesis does not have a matching close parenthesis")},

Results with current code

expected: *errors.errorString(&errors.errorString{s:"open parenthesis does not have a matching close parenthesis"})
actual  : <nil>(<nil>)

expected: <nil>(<nil>)
actual  : []spdxexp.token{spdxexp.token{role:0x0, value:"("}, spdxexp.token{role:0x3, value:"MIT"}}