keyboard: Fix fallback layout when using variants
Commit c1ec7b2f meant to fall back to the base layout in case
a variant like fr+oss
is set up, but as we are checking for
'+' on the array rather than the layout name, the fallback only
"works" for a layout that is literally called '+', whoops.
Fixes #2471 (closed)
Edited by Florian Müllner