minor, refuse to operate on a dirty file in non-rdonly mode

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, PEBKAC, if --into mode doesn't work for ute-mux don't resort to O_TRUNC

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

* core/streaming-mode:
  fix, PEBKAC, if --into mode doesn't work for ute-mux don't resort to O_TRUNC
  minor, refuse to operate on a dirty file in non-rdonly mode