Fix WebImage with indicator, when quick scroll without cache, may cause recursion

[dreampiggy]

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// There are race condition when quick scroll, because SwiftUI handle for that @Published property // Indicator modifier code go into `if` condition and trigger `WebImage.body` (*) // Previous View struct call `onDisappear` and cancel the currentOperation // currentOperation then call error block, and isLoading = true again // isLoading true again trigger another new indicator, go into `else` condition and `Indicator.builder` // Current View struct loaded finished, call isLoading = true again // goto (*)