Fix message when maxSaleQty is set and qty is more than maxSaleQty

[XxXgeoXxX]

Original Isuue #354

Description (*)

When maxSaleQty is set and qty is more than maxSaleQty the "The most you may purchase is %1." message should be sent instead of "Internal server error"
Test Execution
Scenario: https://app.hiptest.com/projects/114163/test-plan/folders/801154/scenarios/2692157

Preconditions (*)

1. Simple Product is created

Manual testing scenarios (*)

Steps to reproduce (*)

1. Go to Stores->Configuration->Catalog->Inventory
2. Open tab "Product Stock Options"
3. Change "Manage Stock" to "Yes"
4. Change "Maximum Qty Allowed in Shopping Cart" to 3
5. Click button "Save config"
6. Go to Store -> Cache Management
7. Click button Flush Magento Cache
8. Create empty cart with GraphQL (or just remove all the products from shopping cart)
9. Perform query

mutation {
addSimpleProductsToCart(
input: {
cart_id: "{{ CART_ID }}",
cartItems: [
{
data: {
sku: "simple-1",
qty: 4
},
}
]
}
) {
cart {
items {
id
qty
product {
sku
name
}
}
}
}
}

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[naydav]

@XxXgeoXxX
Please, take a decision from
https://github.com/magento/graphql-ce/pull/368/files#diff-f18ecfd230e9030db00e9b5006eb519d

Also, need to add one more case to
https://github.com/magento/graphql-ce/pull/368/files#diff-ac800d642d80e0833991eab9f33bdccd

Thanks

[XxXgeoXxX]

Hi @naydav
Could you review?

[ghost]

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