Add bug reproduction for @skip and error

[tobias-tengler]

It appears that the PathHelper can not construct a path, if the first subselection of the parent field is skipped in Fusion. An error is produced for the following query:

query Test($skip: Boolean!) {
 productById(id: "1") {
   skippedField @skip(if: $skip)
   brand {
     errorField
   }
 }
}

The subgraph resolving the Brand.errorField produces an error for it. The Resolve node then tries to extract the error from the subgraph and transform it into an error with a proper path. For this it tries to construct the parent path within the Fusion query selection: https://github.com/ChilliCream/graphql-platform/blob/1f04850d8e2a99637e35835b453ea2591a7c2755/src/HotChocolate/Fusion/src/Core/Execution/ExecutionUtils.cs#L512

The PathHelper then throws an exception because a field is uninitialized: https://github.com/ChilliCream/graphql-platform/blob/1f04850d8e2a99637e35835b453ea2591a7c2755/src/HotChocolate/Core/src/Execution/Processing/PathHelper.cs#L96-L103

I assume the skipped field in the middle messes with something, because it will never be initialized if skipped: https://github.com/ChilliCream/graphql-platform/blob/1f04850d8e2a99637e35835b453ea2591a7c2755/src/HotChocolate/Fusion/src/Core/Execution/ExecutionUtils.cs#L64-L67