Correction of d03e2c98ea

Fix Conjunction.addOperator to do nothing if term is empty
prevent to result in query string with repeated logical operator
like "field:term AND AND field:term"
possibliy causing out of mem in postprocessing_doublecontent

source/net/yacy/cora/federate/solr/logic/AbstractOperations.java

@@ -27,7 +27,7 @@ public abstract class AbstractOperations extends AbstractTerm implements Operati
      */
     @Override
     public void addOperand(Term term) {
-        if (term.toString().isEmpty()) {
+        if (!term.toString().isEmpty()) {
             this.terms.add(term);
         }
     }