Parsing fails if no FI data

[jonlidgard]

Some ofx files do not include FI information (e.g. Barclays Bank). Following code in Finance.swift makes FI parsing optional
/// Information about the entity which provided the OFX file.
public struct Institute: Information {
static let label: String = "FI"

/// The name of the institution.
public var name: String = ""

/// An identifier for this specific institution.
public var id: Identifier = ""

init?(parent element: Element) {
if let element = element[Institute.label] {
name = element["ORG"]?.content ?? ""
id = element["FID"]?.content ?? ""
}
}
}