cpu_group_find_highest_id does not return the expected value

cpu_group_find_highest_id returns -1 when the cpu_list of the group has data instead of advancing to the loop

Lines 54 to 55 in 804ae0c

    
           if (!group || group->cpu_list) 
        
              return(-1);

This function is never used so it does not affect dynamips behavior.

Discovered while converting to rust.