Using startLoadingBeforeViewAppear() with a nil URL causes a memory leak and high cpu

[BobbyRohweder]

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Issue Description

What

A memory leak and 100% cpu occurs from a loop caused by using startLoadingBeforeViewAppear() on a KFImage with a nil url.

Each time the view body is called, the "binder.start" is called and fails the initial context.source guard, which then triggers objectWillChange, and then restarts the loop of attempting to re-render the body. This continues to happen since "loadingOrSucceeded" will always return false for nil URLs.

Reproduce

Example code:

let optionalImageURL: URL? = nil
KFImage(optionalImageURL)
    .startLoadingBeforeViewAppear()

Call stack:

#0 in closure #1 in KFImage.ImageBinder.start<τ_0_0>(context:) at SwiftUI/ImageBinder.swift:61
#1 in closure #2 in CallbackQueue.execute(_:) at Utility/CallbackQueue.swift:54
#2 in OS_dispatch_queue.safeAsync(_:) at Utility/CallbackQueue.swift:78
#3 in CallbackQueue.execute(_:) at Utility/CallbackQueue.swift:54
#4 in KFImage.ImageBinder.start<τ_0_0>(context:) at SwiftUI/ImageBinder.swift:55
#5 in closure #1 in KFImageRenderer.body.getter at SwiftUI/KFImageRenderer.swift:41

Other Comment

Kingfisher version: 7.5.0
iOS version: 16.X