check_outfile: Check output filename
Description
This function checks if an output filename is not NULL
in conjunction
whether the user would like to return an image
Usage
check_outfile(outfile, retimg, fileext = ".nii.gz")
Value
Filename of output file or a temporary filename
Arguments
- outfile
output filename or NULL
- retimg
Should an image be returned
- fileext
a non-empty character vector giving the file extension