Bug 998106 - [B2G][Gaia][FTE][Keyboard] Selecting languages other than
 English during the FTE causes the associated keyboard not to load.
  - Filter out "language to layouts mappings" if the layout is not
    preloaded.
Merge pull request #25647 from RudyLu/build/Bug998106-filter_keyboard_default_layout

Bug 998106 - [B2G][Gaia][FTE][Keyboard] Selecting languages other than English during the FTE causes the associated keyboard not to load.
r=cctuan.