By Essi Lehto and Anne Kauranen ROVANIEMI/HELSINKI (Reuters) – Russia’s invasion of Ukraine has not caught Finland unprepared. Even the Santa Claus theme park in his “hometown” in the snowy north is ready to stand down its elves and revert to its original function – an emergency bomb shelter in case of attack. Tens of thousands of people visit the Santa Park in Rovaniemi city in Lapland each year to meet Santa and have their photograph taken with him. The cavernous underground corridors are replete with Santa’s post office, elf school, handicraft shops, Christmas trees and reindeer. Its main p…