Feature Index disappearing on map moves

[prushforth]

Steps to reproduce:

Enable feature indexing on extension:

Load this page

Click on the map with your mouse

-- feature index appears

Drag the map < 1cm

Expected behaviour

-- if reticle encompasses different features, set of features in the index changes accordingly

Observed behaviour:

-- reticle disappears
-- feature index disappears

[yhy0217]

Resolved in 1ccf354 and #873