Cleanup the single file check in Handler::process()
Cleanup the single file check in Handler::process()

The $isSingle variable is used only after Arr::normalizeFiles() so at
that point the code might as well just check for the array size.

This makes the code more readable.

Also use array_pop() instead of $files[0] to cover the case of
associative arrays.

bkzhn/upload,siriusphp/upload