#i124131# use smart pointer's bool operator instead of comparing its content against NULL

this makes the code more typesafe and avoids the -Wnull-conversion warnings
seen with boost>=1.55 smart pointers in C+11 enabled build environments


git-svn-id: https://svn.apache.org/repos/asf/openoffice/trunk@1562080 13f79535-47bb-0310-9956-ffa450edef68