WhisperBack saves empty files in offline mode

Originally created by @hybridwipe on #11133 (Redmine)

I was debugging a networking issue on one of my machines and attempted to save a debugging file (both in /home/amnesia and to a usb drive), but in both cases, an empty (0 byte) file was created.

I’ve also verified that on a second machine without a network cable plugged in.

To reproduce:
Boot tails on a machine without networking, or disable in greeter.
Run whisperback
Filling in fields
Click submit, dismiss warning about no network
Click submit again, it will offer to save to a local file.
Choose yes, and attempt to save somewhere.

Result:
0 byte file

Expected result:
Debugging info in plain/encrypted text for submission via another machine.

Using Tails 2.0.1