Default engine always used for loaded queries

[Nielswps]

When a query is loaded from an existing project, it is always assigned the default engine, despite another engine being specified in the Queries.json file

How to reproduce

• Setup at least two engines
• Have an existing project with queries
• Assign an engine to at least one query and save it
• Set the engine NOT assigned to the query as the default
• Reload the project

The query is now assigned the new default engine instead of the one specified in the JSON file

Originally posted by @Nielswps in #136 (comment)