fix for when the user hits cancel

git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@3820 6c8d7289-2bf4-0310-a012-ef5d649a1542

htroot/CrawlStartExpert_p.html

@@ -73,7 +73,7 @@
           <td><label for="crawlingFilter">Crawling Filter</label>:</td>
           <td>
 			<input name="crawlingFilter" id="crawlingFilter" type="text" size="20" maxlength="100" value="#[crawlingFilter]#" />
-			<input type="button" value="only one domain" onclick='var domain=prompt("please enter domain without \"www.\" (i.e. \"yacy.net\").");document.getElementById("crawlingFilter").value=".*\\."+domain.replace("\.", "\\.")+"/.*"' />
+			<input type="button" value="only one domain" onclick='var domain=prompt("please enter domain without \"www.\" (i.e. \"yacy.net\").");if(domain!=null){document.getElementById("crawlingFilter").value=".*\\."+domain.replace("\.", "\\.")+"/.*"}' />
 		  </td>
           <td>
             This is an emacs-like regular expression that must match with the URLs which are used to be crawled.