check-qdict: Test termination of qdict_array_split()

qdict_array_split() should terminate if it encounters both an entry with
a key of "%u" and entries with keys prefixed "%u." for the same index.

This patch adds a test for this case.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
