Thailand to demand proof of health insurance for 'risky' long-term visitors   FILE photo   BANGKOK (Reuters) - Foreigners in the “risky” over-50 age group will have to present proof of health insurance when applying for Thai long-term non-immigrant visas, a minister said on Wednesday, so the government doesn’t have to pick up their medical bills.   The rule takes effect at the end of the month to ensure the visitors can afford treatment during a maximum one-ye