Fixing bug free items + Grammar mistake

"We could retrieve the price ..." should've been "We couldn't retrieve the price ..."
Also, this shound support free stuff, and up until some time ago, it actually did.
All code was still written to do this, except that canPurchaseItem() didn't count on free stuff.
Now whenever it's a free (takeable) item the player doesn't own yet, it'll also allow it.
Merge pull request #35 from einsteinK/patch-8

Fixing bug free items + Grammar mistake