validate_cols: validate argument 'cols' in new_file_structure_*()
In a-maldet/readall: Read FWF, DSV, EXCEL And SAS Files

validate argument cols in new_file_structure_*()

1	validate_cols(cols, file_type, sep_width = NULL, err_h)

`cols`	A list object, where each entry represents a column definition. Each element of the list, is a list itself with possible entries: `name`: Column name (optional) `type`: Colunn type (required) `start`: Column start postition (optional and only for FWF) `end`: Column end postition (optional and only for FWF) `width`: Column width (optional and only for FWF)
`file_type`	A character string holding the current file_type.
`sep_width`	An optional string argument, defining the given `sep_width` argument in the FWF-Specification. If the file type is not FWF than it can be omitted.
`err_h`	An error handler. find first column that is not skipped