qadevOOo: use String.length()==0 instead of String.equals(empty string)

Change-Id: I5cdd1fb4fe77c7fc9614f2a6de8995d98d60b551
Reviewed-on: https://gerrit.libreoffice.org/11368
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>