Validate search form of 404 page

I missed to add validate check for it when I added it for the main menu

templates/404.html

@@ -20,7 +20,7 @@ Page does not exist at {{ SITENAME|striptags }} blog.
         <p>Sorry, but the page you are looking for cannot be found. It seems that the page you were trying to reach doesn't exist, or may be it has just moved, or it no longer exists.</p>
         <p>The best thing to do is to use the search form or start again from the <a href="{{ SITEURL }}">home page</a>.</p>
         <div class="input-append">
-            <form action="{{ SITEURL }}/search.html">
+            <form action="{{ SITEURL }}/search.html" onsubmit="return validateForm()">
                 <input type="text" class="span12" placeholder="Search" name="q" id="tipue_search_input">
                 <button class="btn" type="button">Search</button>
             </form>