Added test case for bug #886151

- The exception is the very same as in that report:

  NoMethodError:
  undefined method `[]' for nil:NilClass
    # Product.rb:235:in `get_property'
    # Product.rb:216:in `set_property'
    # Product.rb:207:in `fill_up_relnotes'
    # Product.rb:104:in `FindBaseProducts'
Making sure that @product is defined in get_property

- Defining an empty product if needed
- Adapted test case to what it really returns
New version and new changes file entry
Enhanced function description

- @return
Merge pull request #266 from kobliha/Product-get_property_issue

Fixed Product.get_property issue