Request same url several times

I encountered a problem. When the image is downloading I close the activity, then reopen it, the image will download twice. Also, in RecyclerView when I scroll the list up and down quickly, some Images will download several times. This is a demo for this bug. https://github.com/binwin20/frescoDemo

This is issue is the same as https://github.com/facebook/fresco/issues/587, but can't reopen that issue, so open a new one.

Initialization:
```kotlin
class DemoApp:Application() {
override fun onCreate() {
super.onCreate()
Fresco.initialize(this)
}
}
```
Set Image url:
```kotlin
class SecondActivity: Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_second)
val draweeView: SimpleDraweeView = findViewById(R.id.image_view)
draweeView.setImageURI(Constant.URL)
}
}
```
Requests in Charles: