Save strlen as a variable before loop in cvrf_eval.c
Save strlen as a variable before loop in cvrf_eval.c

The index variable was being compared to strlen inside a while loop,
which causes the loop to calculate strlen each time. This was changed
so that strlen only has to be called once

OpenSCAP/openscap,jan-cerny/openscap,OpenSCAP/openscap,mpreisler/openscap,mpreisler/openscap,jan-cerny/openscap,mpreisler/openscap,OpenSCAP/openscap,redhatrises/openscap,redhatrises/openscap,OpenSCAP/openscap,redhatrises/openscap,jan-cerny/openscap,mpreisler/openscap,OpenSCAP/openscap,redhatrises/openscap,jan-cerny/openscap,redhatrises/openscap,OpenSCAP/openscap,jan-cerny/openscap,mpreisler/openscap,redhatrises/openscap,jan-cerny/openscap,mpreisler/openscap