Improve raster reprojection behavior when tiles fail to load

src/ol/reproj/tile.js

@@ -254,6 +254,9 @@ ol.reproj.Tile.prototype.reproject_ = function() {
   }, this);
   this.sourceTiles_.length = 0;
 
+  if (sources.length === 0) {
+    this.state = ol.TileState.ERROR;
+  } else {
     var z = this.wrappedTileCoord_[0];
     var size = this.targetTileGrid_.getTileSize(z);
     var width = goog.isNumber(size) ? size : size[0];
@@ -269,6 +272,7 @@ ol.reproj.Tile.prototype.reproject_ = function() {
         this.renderEdges_);
 
     this.state = ol.TileState.LOADED;
+  }
   this.changed();
 };