Don't call copy function if its argument is -1 because "firefox" isn't present in searchTerm

There's still at least 1 other case to deal (eg: ../en-US/ as indicated in bugreport)

Change-Id: Id78ec6c174abecd9cc101ac730f5e83b5acd167d
Reviewed-on: https://gerrit.libreoffice.org/28271Reviewed-by: Susobhan Ghosh <susobhang70@gmail.com>
Tested-by: Julien Nabet <serval2412@yahoo.fr>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>