skip xulG.get_barcode if no barcode completion

For Check In and Check Out interfaces, skip the xulG.get_barcode call if there
are no active Barcode Completion entries (under Admin->Local Administration->
Barcode Completion) at the time of the staff client login sequence.

However, for Check Out, an exception is made if the "Load patron from Checkout"
library setting is in effect, since that functionality depends on
xulG.get_barcode.

Signed-off-by: Jason Etheridge <jason@esilibrary.com>
Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>