BibUpload: FFT -c now appends unexisting docnames

• If FFT correct is performed on an unexisting docname, this had cause an ERROR in the past, because it was not possible to revise an unexisting bibdoc. However this was contrasting with the implementation of BibUpload -c mode for metadata tags, where if a tag did not exist it was appended. This patch makes the behaviour uniform and FFT correct of an unexisting docname now creates a new bibdoc.