logging: use dummy handler when CLI logging is disabled instead of None
logging: use dummy handler when CLI logging is disabled instead of None

This makes the code cleaner by removing conditionals and making the CLI
and file logging completely analogous.

Doesn't affect performance.

nicoddemus/pytest,markshao/pytest,Akasurde/pytest,pytest-dev/pytest,nicoddemus/pytest,The-Compiler/pytest,The-Compiler/pytest,RonnyPfannschmidt/pytest