"Inefficient usage of string::find() in condition; string::compare() would be faster."

Change-Id: I90403b1d05eff6499c10be33068e5fd4fed30b62
Reviewed-on: https://gerrit.libreoffice.org/19966Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>