26, 27 and 28 of Insurance Contracts Act 1984 (Cth), alleged misrepresentation by insured, indemnity, Insurance, insurer’s decision to underwrite, no rights under s 28(3), operation of ss 21, rights of insurer, significance of certain disclosures in a confusing renewal questionnaire, waiver by insurer, whether there was any relevant misrepresentation or failure to disclose