Merge pull request #49 from mapbox/multi-index

Query from `map` table with more than one index.

lib/zxystream.js

@@ -33,7 +33,7 @@ ZXYStream.prototype._read = function() {
     if (!stream.table) {
         return this.source._db.get("select count(1) as count from sqlite_master where type = 'index' and tbl_name = 'map';", function(err, row) {
             if (err) return stream.emit('error', err);
-            stream.table = row.count === 1 ? 'map' : 'tiles';
+            stream.table = row.count >= 1 ? 'map' : 'tiles';
             return stream._read();
         });
     }