fix, make sure sluts start behind the header, truncate the file if necessary

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
hygiene, rely on stat object once only

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
test, provide regression for empty ute files, impl'd via empty uta mux

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/file' into next

* core/file:
  test, provide regression for empty ute files, impl'd via empty uta mux
  hygiene, rely on stat object once only
  fix, make sure sluts start behind the header, truncate the file if necessary