fix exporting twice on pressing the Enter key

[sssoleileraaa]

Description

Fixes #1240

Test Plan

1. Export a file, any file, just press the Enter key (instead of clicking the Continue button) after typing in the password to unlock your luks-encrypted export device.
2. See that the file is no longer exported twice

Review issue #1240 and see if there are other ways to trigger a double export.

[eloquence]

I will attempt to reproduce the original issue now, and will review if the fix resolves all cases I can reproduce.

[eloquence]

I'm able to consistently reproduce the double-export by pressing [Enter] on the password dialog, and was only sporadically seeing it before. I guess that identifies me as more of a clicky-clicky user than Conor and Mickael, not that more evidence was needed. ;-) Will now try other mouse/keyboard combos.

[eloquence]

As expected, using mouse-only navigation for everything but the passphrase entry results in a single file. Using keyboard-only navigation for everything but the password submit button also results in a single file. Now testing the fix.

[eloquence]

With the fix in place, I am no longer able to reproduce the issue when using [Enter], and am observing no regressions when using the mouse. This one was pretty elusive, but I think you got it :-)

[sssoleileraaa]

Thanks for taking it out for a spin!

[emkll]

Thanks @creviera changes look good to me visually, went through the test plan and no longer observed a double export with these changes.