magit-reverse-files: Guard against empty section list
magit-reverse-files removes binary files from `sections', so it may end up nil. At the time this code was introduced, passing nil to magit-reverse-apply wasn't an issue, but it leads to a type error in magit-apply-patch since ddce6ce4 (sections: Use oref instead of dedicated slot accessors, 2018-01-17). Note: magit-discard-files--discard performs a similar removal of binary files, but it doesn't lead to a type error because it already guards against the nil case.
Showing with 4 additions and 3 deletions