fix: bug safeTransferFrom(address,address,uint256) charge royalty twice

[EasonC13]

Dear EatTheBlocks

I notice a little bug in the royalty contract example that will charge the royalty fee twice. So I fix it and add the test code. Then create this PR.

P.S. I really appreciate you for making these videos.

[vercel[bot]]

Someone is attempting to deploy a commit to a Personal Account owned by @jklepatch on Vercel.

@jklepatch first needs to authorize it.