Description preview should be enabled even if syntax highlighting is disabled

For instance, use PegDown Formatter and enable SUPPRESS_ALL_HTML.

changelog.html

@@ -55,7 +55,8 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
-  <li class=>
+  <li class=bug>
+    Description preview and syntax highlighting broken since 1.477.
 </ul>
 </div><!--=TRUNK-END=-->
 

core/src/main/resources/lib/form/textarea.jelly

@@ -71,9 +71,11 @@ THE SOFTWARE.
 
   <f:prepareDatabinding />
   <j:set var="value" value="${attrs.value ?: instance[attrs.field] ?: attrs.default}" />
+  <j:if test="${attrs['previewEndpoint']!=null || attrs['codemirror-mode']!=null}">
+    <st:adjunct includes="lib.form.textarea.textarea"/>
+  </j:if>
   <j:if test="${attrs['codemirror-mode']!=null}">
     <st:adjunct includes="
-        lib.form.textarea.textarea,
         org.kohsuke.stapler.codemirror.mode.${attrs['codemirror-mode']}.${attrs['codemirror-mode']},
         org.kohsuke.stapler.codemirror.theme.default"/>
   </j:if>