Fix unknown variable warning

veryplaintxt/sidebar.php

@@ -12,7 +12,7 @@
 					<h3><label for="s"><?php _e('Search', 'veryplaintxt') ?></label></h3>
 					<form id="searchform" method="get" action="<?php bloginfo('home') ?>">
 						<div>
-							<input id="s" name="s" type="text" value="<?php echo wp_specialchars(stripslashes($_GET['s']), true) ?>" size="10" />
+							<input id="s" name="s" type="text" value="<?php if(array_key_exists($_GET, 's')) { echo wp_specialchars(stripslashes($_GET['s']), true) } ?>" size="10" />
 							<input id="searchsubmit" name="searchsubmit" type="submit" value="<?php _e('Find', 'veryplaintxt') ?>" />
 						</div>
 					</form>