PSR2/SwitchDeclaration: update doc as case body should be non-empty

This commit updates the valid and invalid code examples in a
`<code_comparison>` block, as the `There must be a comment when
fall-through is intentional in a non-empty case body` error is only
triggered for non-empty `case` bodies. It also fixes the positioning of
the `<em>` tags in the modified code examples.

Author: rodrigoprimo

src/Standards/PSR2/Docs/ControlStructures/SwitchDeclarationStandard.xml

@@ -67,8 +67,9 @@ switch ($foo) {
         <![CDATA[
 switch ($foo) {
     case 'bar':
-    <em>// no break</em>
-    default<em></em>:
+        echo $foo;
+        <em>// no break</em>
+    default:
         break;
 }
         ]]>
@@ -77,7 +78,8 @@ switch ($foo) {
         <![CDATA[
 switch ($foo) {
     case 'bar':
-    default<em></em>:
+        echo $foo;<em></em>
+    default:
         break;
 }
         ]]>