filetable: Fix replacing a file with itself
filetable: Fix replacing a file with itself

Previously this would incorrectly decrement the reference count.

bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6