ir_flatir_flatten_clean takes an object of class ir_flat and either
returns all non-empty spectra or all empty spectra as object of class
ir_flat.
ir_flat_clean(x, return_empty = FALSE)x where empty spectra are dropped (if return_empty = TRUE) or
only empty spectra are returned (return_empty = FALSE).
An object of class ir_flat.
A logical value indicating if the empty spectra should be
returned (return_empty = TRUE) or the non-empty spectra
(return_empty = FALSE).