The KJV wouldn't be cursed, but if folks intentionally added verses to Scripture, they would be accursed.
I don't think it was intentional. I think earlier owners of manuscripts added marginal notes that got included in the copies that were made by others.
But, in essence, what you have is a puzzle with a bunch of extra pieces in it. Those extra pieces are largely marginal notes, etcetera, that got copied in subsequent copies.
The entire verse is found in the Majority of all manuscripts, including D, E, F, G, H, I, K, M, N, S, U, V, W, X,Y, Sigma, Phi and Omega. It is the reading in the Old Latin copies a, aur, b, d, f, ff2, g1, l, n, q, r1 and r2.
It is also found in the Latin Vulgate, the Syriac Peshitta, Curetonian, Herclean, Coptic Boharic, Armenian, Georgian and Ethiopian ancient versions. It was also included in the Greek Diatessaron 160-175 A.D.
It is quoted by such early church writers as Hilary, Chrysostom, Chromatius and Augustine.
Westcott and Hort completely omitted the entire verse from their critical Greek text. And this is mainly because the verse is not found in Sinaiticus, or Vaticanus, and only a handful of other manuscripts.
You should get you a Bible that has all the verses, for man should not live by bread alone, but be every word that proceeded out of the mouth of God.