Stop filetest ops from calling FETCH on parent op’s arg

Stop filetest ops from calling FETCH on parent op’s arg

This is a regression in 5.14.0.

Commit 6f1401dc made ops call get-magic before overloading, but it
ended up making filetest ops call get-magic on the topmost item of the
stack even if the filetest op was not going to use the stack (which
happens for ‘-r bareword’ and plain ‘-r’).

This would affect cases like:

  push @foo, $tied, -r;