commit 642107a2 attempts to avoid resetting the current keymap on
spurious input source changes.
It does this by checking if the current layout id is found in
the new list of layouts and resetting the current layout to the
associated match in the list. By not nullifying the current
layout, it won't get subsequently reset.
Unfortunately, if the order of the list changes, resetting the
current keymap is still necessary, since the order corresponds
with the index of the activated group.
This commit changes the code to nullify the current layout if
its group index changes.
https://bugzilla.redhat.com/show_bug.cgi?id=1573923
2997e4950b