Fix empty text node for emphasis after task

Related to: remarkjs/react-markdown#494.

from-markdown.js

@@ -23,9 +23,13 @@ function exitParagraphWithTaskListItem(token) {
   ) {
     // Must start with a space or a tab.
     head.value = head.value.slice(1)
-    head.position.start.column++
-    head.position.start.offset++
-    node.position.start = Object.assign({}, head.position.start)
+    if (head.value.length === 0) {
+      node.children.shift()
+    } else {
+      head.position.start.column++
+      head.position.start.offset++
+      node.position.start = Object.assign({}, head.position.start)
+    }
   }
 
   this.exit(token)

test.js

@@ -140,6 +140,28 @@ test('markdown -> mdast', function (t) {
     'should not support a task list item when not in a list item'
   )
 
+  t.deepEqual(
+    removePosition(
+      fromMarkdown('* [x] *b*', {
+        extensions: [syntax],
+        mdastExtensions: [taskListItem.fromMarkdown]
+      }),
+      true
+    ).children[0].children[0],
+    {
+      type: 'listItem',
+      spread: false,
+      checked: true,
+      children: [
+        {
+          type: 'paragraph',
+          children: [{type: 'emphasis', children: [{type: 'text', value: 'b'}]}]
+        }
+      ]
+    },
+    'should support a text construct after the checkbox'
+  )
+
   t.end()
 })