Crash when dropping an image outside of sandbox
When dropping an image onto the window that isn't accessible in the Flatpak sandbox, Obfuscate hard crashes.
To reproduce:
- Put an image in a folder inaccessible, such as ~/Pictures
- Drag the image and drop it onto the window
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { domain: g-file-error-quark, code: 4, message: "Failed to open file “/var/home/pluto/Pictures/Screenshot from 2019-04-11 09-44-12.png”: No such file or directory" }', src/libcore/result.rs:999:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.