make sure worker sends response after reloading 'empty' tile

src/source/vector_tile_worker_source.js

@@ -110,6 +110,8 @@ class VectorTileWorkerSource implements WorkerSource {
             delete this.loading[uid];
 
             if (err || !response) {
+                workerTile.status = 'done';
+                this.loaded[uid] = workerTile;
                 return callback(err);
             }
 
@@ -163,7 +165,12 @@ class VectorTileWorkerSource implements WorkerSource {
             if (workerTile.status === 'parsing') {
                 workerTile.reloadCallback = done;
             } else if (workerTile.status === 'done') {
-                workerTile.parse(workerTile.vectorTile, this.layerIndex, this.actor, done);
+                // if there was no vector tile data on the initial load, don't try and re-parse tile
+                if (workerTile.vectorTile) {
+                    workerTile.parse(workerTile.vectorTile, this.layerIndex, this.actor, done);
+                } else {
+                    done();
+                }
             }
         }
     }

test/unit/source/vector_tile_worker_source.test.js

@@ -58,6 +58,7 @@ test('VectorTileWorkerSource#reloadTile reloads a previously-loaded tile', (t) =
     source.loaded = {
         '0': {
             status: 'done',
+            vectorTile: {},
             parse
         }
     };
@@ -79,6 +80,7 @@ test('VectorTileWorkerSource#reloadTile queues a reload when parsing is in progr
     source.loaded = {
         '0': {
             status: 'done',
+            vectorTile: {},
             parse
         }
     };
@@ -112,6 +114,7 @@ test('VectorTileWorkerSource#reloadTile handles multiple pending reloads', (t) =
     source.loaded = {
         '0': {
             status: 'done',
+            vectorTile: {},
             parse
         }
     };
@@ -152,6 +155,27 @@ test('VectorTileWorkerSource#reloadTile handles multiple pending reloads', (t) =
     t.end();
 });
 
+test('VectorTileWorkerSource#reloadTile does not reparse tiles with no vectorTile data but does call callback', (t) => {
+    const source = new VectorTileWorkerSource(null, new StyleLayerIndex());
+    const parse = t.spy();
+
+    source.loaded = {
+        '0': {
+            status: 'done',
+            parse
+        }
+    };
+
+    const callback = t.spy();
+
+    source.reloadTile({ uid: 0 }, callback);
+    t.ok(parse.notCalled);
+    t.ok(callback.calledOnce);
+
+    t.end();
+});
+
+
 test('VectorTileWorkerSource provides resource timing information', (t) => {
     const rawTileData = fs.readFileSync(path.join(__dirname, '/../../fixtures/mbsv5-6-18-23.vector.pbf'));