Buffer overflow in `R_GenerateLookup`

[Rua]

Version of Chocolate Doom: current master

Concerning the following line of the R_GenerateLookup function:

colofs[x] = LONG(realpatch->columnofs[x-x1])+3;

The columnfs field of the patch_t struct is a statically sized array of length 8. But the index x-x1 is often greater than 7, so it indexes past the end of the array. This was there in the original Id source code too, apparently never caused problems?