fix NPE in IndexControlRWIs_p.html

- metatags my be null
Caused by: java.lang.NullPointerException
	at net.yacy.search.query.QueryParams.getFacets(QueryParams.java:445)
	at net.yacy.search.query.QueryParams.getBasicParams(QueryParams.java:400)
	at net.yacy.search.query.QueryParams.solrTextQuery(QueryParams.java:345)
	at net.yacy.search.query.QueryParams.solrQuery(QueryParams.java:334)
	at net.yacy.search.query.SearchEvent.<init>(SearchEvent.java:290)
	at net.yacy.search.query.SearchEventCache.getEvent(SearchEventCache.java:176)
	at IndexControlRWIs_p.genSearchresult(IndexControlRWIs_p.java:641)
	at IndexControlRWIs_p.respond(IndexControlRWIs_p.java:141)

source/net/yacy/search/query/QueryParams.java

@@ -442,10 +442,11 @@ public final class QueryParams {
         }
 
         // add vocabulary facets
-        for (Tagging.Metatag tag: this.metatags) {
-            fq.append(" AND ").append(CollectionSchema.VOCABULARY_PREFIX).append(tag.getVocabularyName()).append(CollectionSchema.VOCABULARY_SUFFIX).append(":\"").append(tag.getObject()).append('\"');
+        if (this.metatags != null) {
+            for (Tagging.Metatag tag : this.metatags) {
+                fq.append(" AND ").append(CollectionSchema.VOCABULARY_PREFIX).append(tag.getVocabularyName()).append(CollectionSchema.VOCABULARY_SUFFIX).append(":\"").append(tag.getObject()).append('\"');
+            }
         }
-        
         // add author facets
         if (this.modifier.author != null && this.modifier.author.length() > 0 && this.solrSchema.contains(CollectionSchema.author_sxt)) {
             fq.append(" AND ").append(CollectionSchema.author_sxt.getSolrFieldName()).append(":\"").append(this.modifier.author).append('\"');