The application is restarted if it was sent to the background using the "Back" button and brought back

[Softvision-MariusComan]

[Notes]:

• If it is intended to close the application when the "Back" button is tapped, after the first tap on it, we should display a warning message in order to inform the user that the application will be closed.

[Affected Platforms]:

• Android 8.0 (Samsung S8)
• Android 8.0 (Google Pixel) Huawei P20 Lite
• Android 8.0 (Huawei P20 Lite)

[Prerequisites]:

• Have the latest Send Android build (org.mozilla.sendandroid-2019-02-06-signed.apk)

[Steps to reproduce]:

1. Open the Send Android application.
2. Tap the “Add file(s)” button and add any file.
3. Tap the "Upload" button and after that tap the device's "Back' button.
4. Bring back the application from the background and observe the behavior.

[Expected result]:

• The upload process is still running or the file was uploaded.

[Actual result]:

• The application is restarted and the upload process is canceled.

[Additional notes]:

• This issue is also reproducible if the "Change Aspect Ratio" button is tapped instead of the "Back" button on the Samsung S8 device.
• This issue is not reproducible if the application was sent to the background using the "Home" button.
• Here you can find the logs.
• Attached a screen recording of the issue: