Really skip CDB_TableMetadata lookup for sql affected by no tables

Closes #169

NEWS.md

@@ -1,6 +1,10 @@
 1.8.4 -- 2014-03-DD
 -------------------
 
+Enhancements:
+
+ - Really skip CDB_TableMetadata lookup for sql affected by no tables (#169)
+
 1.8.3 -- 2014-02-27
 -------------------
 

lib/cartodb/server_options.js

@@ -193,7 +193,7 @@ module.exports = function(){
           }
           var qtables = rows[0].cdb_querytables;
           var tableNames = qtables.split(/^\{(.*)\}$/)[1];
-          tableNames = tableNames.split(',');
+          tableNames = tableNames ? tableNames.split(',') : [];
           callback(null, tableNames);
       });
     };