Do not execute `FetchCartItems` if there is no item

[NicolasMahe]

Currently, if there is no item in the cart, the query FetchCartItems is executed with an empty filter that returns ALL the offer of the platform which takes a very long time.

{
    "operationName": "FetchCartItems",
    "variables": {
        "offerIds": []
    },
    "query": "query FetchCartItems($offerIds: [UUID!]!) {\n  listings(condition: {ids: $offerIds, status: [ACTIVE, EXPIRED]}) {\n    nodes {\n      id\n      type\n      expiredAt\n      maker {\n        address\n        name\n        image\n        verification {\n          status\n          __typename\n        }\n        __typename\n      }\n      unitPrice\n      availableQuantity\n      currency {\n        image\n        id\n        decimals\n        symbol\n        __typename\n      }\n      asset {\n        chainId\n        collectionAddress\n        tokenId\n        collection {\n          chainId\n          address\n          name\n          standard\n          __typename\n        }\n        name\n        image\n        imageMimetype\n        animationUrl\n        animationMimetype\n        __typename\n      }\n      __typename\n    }\n    __typename\n  }\n}"
}

The query should not be executed if the offerIds is an empty array.