Avoid callstack loop by making sure only one geocoder data iterator buffer-flush operation is happening at once

lib/mbtiles.js

@@ -625,7 +625,11 @@ MBTiles.prototype.geocoderDataIterator = function(type) {
     var doneSentinel = {};
     var _this = this;
 
+    var sending = false;
     var sendIfAvailable = function() {
+        if (sending) return;
+        sending = true;
+
         while (nextQueue.length && dataQueue.length) {
             var nextCb = nextQueue.shift(), data;
             if (dataQueue[0] == doneSentinel) {
@@ -637,6 +641,8 @@ MBTiles.prototype.geocoderDataIterator = function(type) {
                 nextCb({value: {shard: data.shard, data: zlib.inflateSync(data.data)}, done: false});
             }
         }
+
+        sending = false;
     }
 
     var refilling = false;