No blank added at EOF when file to style already corresponds to style guide

[lorenzwalthert]

This is because equality check if performed without taking into account if the file has a blank line at the end. The only way to figure this out is to use a lower-level implementation of xfun::read_utf8(), i.e. readLines(), catch the warning (if any) about missing blank line and propagate the information upwards in the call stack. Interacts with #320.