Fix infinite loop for metadata retrieval when composing HdtDatasources

Author: rubensworks

lib/datasources/CompositeDatasource.js

@@ -60,7 +60,7 @@ CompositeDatasource.prototype._getDatasourceById = function(datasourceIndex) {
 CompositeDatasource.prototype._getDatasourceInfo = function(query, absoluteOffset, cb) {
   var self = this;
   var emptyQuery = {
-    offset: 0, limit: 0,
+    offset: 0, limit: 1,
     subject: query.subject, predicate: query.predicate, object: query.object
   };
   return findRecursive(0, absoluteOffset, -1, -1, 0, cb);

test/datasources/CompositeDatasource-test.js

@@ -91,7 +91,7 @@ describe('CompositeDatasource', function () {
     itShouldExecute(getDatasource,
       'a query for an existing predicate',
       { predicate: 'http://example.org/p1', limit: 10, features: { triplePattern: true, limit: true } },
-      10, 220 + 110); // 220 is an inexact count from the HDT files, the 110 from the ttl file is exact.
+      10, 112);
 
     itShouldExecute(getDatasource,
       'a query for a non-existing predicate',