fix crash when package_dir=={'':'python'}
fix crash when package_dir=={'':'python'}

wkentaro/catkin,asmodehn/catkin,meyerj/catkin,thaddeustaylor/catkin,meyerj/catkin,meyerj/catkin,thaddeustaylor/catkin,jack-oquin/catkin,beni55/catkin,thaddeustaylor/catkin,ros/catkin,shyamalschandra/catkin,jack-oquin/catkin,harmishhk/catkin,scpeters/catkin,harmishhk/catkin,ros/catkin,scpeters/catkin,wkentaro/catkin,asmodehn/catkin,jack-oquin/catkin,beni55/catkin,scpeters/catkin,wkentaro/catkin,ros/catkin,asmodehn/catkin,shyamalschandra/catkin,harmishhk/catkin,beni55/catkin,shyamalschandra/catkin