Fix incorrect indices for emphasis marks drawing in InlineTextBox::paint

LayoutTests/fast/text/emphasis-combined-text.html

 <meta charset="utf-8">
 <style>
 html {
     -webkit-writing-mode: vertical-rl;
+    text-rendering: geometricPrecision;
 }
 
 p {
     font-family: "hiragino mincho pron";
     font-size: 48px;
 }
 
 .combine {
     -webkit-text-combine: horizontal;
 }
 
 </style>
 <p>
-    <span  style="-webkit-text-emphasis: sesame red">文字<span class="combine">900</span>年</span>
+    <span  style="-webkit-text-emphasis: sesame red">文字<span class="combine">90</span>年</span>
 </p>
 <p>
-    <span  style="-webkit-text-emphasis: '@' red">文字<span class="combine">900</span>年</span>
+    <span  style="-webkit-text-emphasis: '@' red">文字<span class="combine">90</span>年</span>
 </p>
 <p>
-    <span  style="-webkit-text-emphasis: '年' red">文字<span class="combine">900</span>年</span>
+    <span  style="-webkit-text-emphasis: '年' red">文字<span class="combine">90</span>年</span>
 </p>