Fixes for nft example launchpad.move

[arjanjohan]

This PR solves 2 issues in the launchpad.move example.

Mint stage index from token-minter module

When using this example template, we ran into an issue with the mint stages from token-minter.
minter::execute_earliest_stage loops over the mint stages, and removes any inactive indexes from the mint_stages vector, until it finds and active stage and then returns that index. Since the inactive indexes have been removed, the returned index does not match the active mint stage. The active mint stage will always have index 0, since all earlier indexes have been removed for being inactive.

The launchpad.move module uses returned value from execute_earliest_stage as input for index when calling minter::find_mint_stage_by_index. It should just use 0 as input for index, as that is now the index for the active mint stage.

Check on collection_uri

Also there is no check on collection_uri when creating a collection. This can cause problems later in construct_nft_metadata_uri, where /collection.json is replaced by {next_nft_id}.json. I added a check in create_collection to ensure the collection_uri ends with .json.

[0xaptosj]

taking a look now

[0xaptosj]

@arjanjohan thanks for the fix! do you have twitter? would love to give you a shout-out and buy you a coffee (send you some USDT hehe

[arjanjohan]

@arjanjohan thanks for the fix! do you have twitter? would love to give you a shout-out and buy you a coffee (send you some USDT hehe
yes im arjanjohan on twitter as well. thanks!