Avoid creating first-letter RenderTextFragments for unsuitable text nodes

LayoutTests/editing/selection/extend-by-word-002.html

Index: LayoutTests/editing/selection/extend-by-word-002.html
diff --git a/LayoutTests/editing/selection/extend-by-word-002.html b/LayoutTests/editing/selection/extend-by-word-002.html
index d963877f12a56aad86dfc1906b2aaf0024832c0e..1259c57f58da1f9ff2f7d6674ba51b5389adbf5a 100644
--- a/LayoutTests/editing/selection/extend-by-word-002.html
+++ b/LayoutTests/editing/selection/extend-by-word-002.html
@@ -62,10 +62,10 @@ selection.addRange(range);
 for (var i = 0; i < 6; ++i)
     selection.modify('extend', 'forward', 'word');
 shouldBeEqualToString('selection.type', 'Range');
-shouldBe('selection.anchorNode', '$("test").querySelectorAll("li")[0].childNodes[1].firstChild');
+shouldBe('selection.anchorNode', '$("test").querySelectorAll("li")[0].childNodes[0]');
 shouldBe('selection.anchorOffset', '0');
 shouldBe('selection.focusNode', '$("test").querySelectorAll("li a")[3].firstChild');
-shouldBe('selection.focusOffset', '5');
+shouldBe('selection.focusOffset', '4');
 if (window.testRunner)
     $('container').outerHTML = '';
 </script>