Don't rely on the repository being initialized for sharing.

The share menu item is accessible even while the repository is still
loading; so when accessing it before loading completed there will be a
NPE.
Hardcoding the path isn't a big problem anyway as we
- do this in a lot of places anyway (mainly in the activities where the
  actual objects are loaded in the fragments) and
- we need to rely on the exact path conventions for the browse filter
  anyway