_dbg_ILSimpleGetText, make _dbg_ILSimpleGetText return no value since
  nobody is using it.
- Stop dereferencing a possible NULL in pdump since
  _dbg_ILGetDataPointer can potentially return NULL (for instance for
  root or desktop pidl).
- Make shdebugstr_guid use standard wine_dbg_sprintf instead of the
  handmade solution.