Handle missing password values in command options

[srichs]

Motivation

• Ensure that when a --password (or Windows /password) option is present without a value, code raises a clear ValueError instead of silently returning None or allowing an IndexError later.

Description

• Update _get_password in src/veracrypt/veracrypt.py to treat an empty string as a missing password and to catch an IndexError when the option is present without a following value, raising ValueError in that case.

Testing

• No automated tests were run for this change.

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Codex Task