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

[dreampiggy]

See the comment for reason:

// 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 (*)