Fix vietnamese layout to correctly handle cmd + 1.

In vietnamese layout, cmd + [vkeycode=18] does not print any characters. This
should still be correctly interpretted as a hotkey for cmd + '1'.

Previously, the logic for cr_firesForKeyEvent would early exit when
charactersIgnoringModifiers had 0 length. Subsequent logic would use characters
in place of charactersIgnoringModifiers. This CL moves the latter logic before
the former logic so that if charactersIgnoringModifiers has 0 length, we'll
instead check characters.

Change-Id: I3fcc45579c7697ca843ef3472fa294fa2da02262
Bug: 889424
Reviewed-on: https://chromium-review.googlesource.com/1259342
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596298}
2 files changed