Revert "Handle empty source tiles and queue them properly"

This reverts commit 818bdc411c.

src/ol/TileQueue.js

@@ -112,12 +112,10 @@ class TileQueue extends PriorityQueue {
       if (state === TileState.ABORT) {
         abortedTiles = true;
       } else if (state === TileState.IDLE && !(tileKey in this.tilesLoadingKeys_)) {
+        this.tilesLoadingKeys_[tileKey] = true;
+        ++this.tilesLoading_;
+        ++newLoads;
         tile.load();
-        if (tile.getState() === TileState.LOADING) {
-          this.tilesLoadingKeys_[tileKey] = true;
-          ++this.tilesLoading_;
-          ++newLoads;
-        }
       }
     }
     if (newLoads === 0 && abortedTiles) {

src/ol/source/VectorTile.js

@@ -236,17 +236,15 @@ class VectorTile extends UrlTile {
               empty = false;
               sourceTile.addEventListener(EventType.CHANGE, this.handleTileChange.bind(this));
               sourceTile.load();
-            } else {
-              sourceTile = null;
             }
           } else {
             empty = false;
           }
           covered = false;
-          if (sourceTile === undefined) {
+          if (!sourceTile) {
             return;
           }
-          if (sourceTile !== null && tile.getState() === TileState.IDLE) {
+          if (sourceTile.getState() !== TileState.EMPTY && tile.getState() === TileState.IDLE) {
             tile.loadingSourceTiles++;
             const key = listen(sourceTile, EventType.CHANGE, function() {
               const state = sourceTile.getState();