fixes bug 1017077 - Only make links to home page of valid product names

@rhelmer r?
So we have a default `product` variable which becomes `Firefox` by default. That's what the nav items are about if you're on a page like `/api` or `/about`. However, for `report_index` it would pick up the product from the raw crash and this could be something strange like `Firefox-Trunk` or `83IHGxUh2340fuh234f` and whatever it is we don't want to change the nav to use this product name. 

The original error was that the page would break because the new `product` name was `Firefox-Trunk` and because of the `-` it was not possible to call `reverse('crashstats:home', args=('Firefox-Trunk',))`. So basically we should avoid the product name in the raw crash to build up the links in the nav. 

I did deliberately not test that there's absolute no link with `SummerWolf` in it. I just picked the first one which was the `crashstats:home` link.