Handle empty client rects in LinesYardstick

getBoundingClientRect returns garbage values if the range has zero
width, which it does in the case of a fold placeholder or any other
zero-width character.

Sometimes getClientRects() returns an empty list, so we fall back to the
bounding rect in these cases.

src/lines-yardstick.coffee

@@ -108,4 +108,4 @@ class LinesYardstick
   clientRectForRange: (textNode, startIndex, endIndex) ->
     @rangeForMeasurement.setStart(textNode, startIndex)
     @rangeForMeasurement.setEnd(textNode, endIndex)
-    @rangeForMeasurement.getBoundingClientRect()
+    @rangeForMeasurement.getClientRects()[0] ? @rangeForMeasurement.getBoundingClientRect()