Make react cursor the width of a default character at the end of lines

When the cursor is positioned before a character, we always make it the
width of that character. But at the end of a line, there is no character
to use to set the width, so we just use the defaultCharWidth.

This makes the block cursor visible on empty lines in vim-mode.

src/cursor-component.coffee

@@ -6,10 +6,11 @@ CursorComponent = React.createClass
   displayName: 'CursorComponent'
 
   render: ->
-    {editor, screenRange, scrollTop, scrollLeft} = @props
+    {editor, screenRange, scrollTop, scrollLeft, defaultCharWidth} = @props
     {top, left, height, width} = editor.pixelRectForScreenRange(screenRange)
     top -= scrollTop
     left -= scrollLeft
+    width = defaultCharWidth if width is 0
     WebkitTransform = "translate3d(#{left}px, #{top}px, 0px)"
 
     div className: 'cursor', style: {height, width, WebkitTransform}