post response file error

[rj9676564]

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Issue Info

Info	Value
Platform Name	flutter
Platform Version	1.5.0 / 12.0 / 9.0
Dio Version	4.0.6
Android Studio / Xcode Version	e.g. Android Studio 3.3.2 / Xcode 10.2.1
Repro rate	100%

Issue Description and Steps

post request,upload jpg get back bmp file.

👇：http vs dio