Fix lazy load of RTL text plugin on GeoJSON sources

src/data/bucket/symbol_bucket.js

@@ -521,7 +521,9 @@ class SymbolBucket implements Bucket {
     }
 
     isEmpty() {
-        return this.symbolInstances.length === 0;
+        // When the bucket encounters only rtl-text but the plugin isnt loaded, no symbol instances will be created.
+        // In order for the bucket to be serialized, and not discarded as an empty bucket both checks are necessary.
+        return this.symbolInstances.length === 0 && !this.hasRTLText;
     }
 
     uploadPending() {

src/source/rtl_text_plugin.js

@@ -141,3 +141,12 @@ export const plugin: {
         };
     }
 };
+
+export const lazyLoadRTLTextPlugin = function() {
+    if (!plugin.isLoading() &&
+        !plugin.isLoaded() &&
+        getRTLTextPluginStatus() === 'deferred'
+    ) {
+        downloadRTLTextPlugin();
+    }
+};

src/source/tile.js

@@ -11,6 +11,7 @@ import Texture from '../render/texture';
 import browser from '../util/browser';
 import EvaluationParameters from '../style/evaluation_parameters';
 import SourceFeatureState from '../source/source_state';
+import {lazyLoadRTLTextPlugin} from './rtl_text_plugin';
 
 const CLOCK_SKEW_RETRY_TIMEOUT = 30000;
 
@@ -183,6 +184,7 @@ class Tile {
                 if (bucket instanceof SymbolBucket) {
                     if (bucket.hasRTLText) {
                         this.hasRTLText = true;
+                        lazyLoadRTLTextPlugin();
                         break;
                     }
                 }

src/source/vector_tile_source.js

@@ -9,7 +9,6 @@ import TileBounds from './tile_bounds';
 import {ResourceType} from '../util/ajax';
 import browser from '../util/browser';
 import {cacheEntryPossiblyAdded} from '../util/tile_request_cache';
-import {plugin as rtlTextPlugin, getRTLTextPluginStatus, downloadRTLTextPlugin} from './rtl_text_plugin';
 
 import type {Source} from './source';
 import type {OverscaledTileID} from './tile_id';
@@ -156,15 +155,6 @@ class VectorTileSource extends Evented implements Source {
 
             if (this.map._refreshExpiredTiles && data) tile.setExpiryData(data);
             tile.loadVectorData(data, this.map.painter);
-            if (tile.hasRTLText) {
-                const plugin = rtlTextPlugin;
-                if (!plugin.isLoading() &&
-                    !plugin.isLoaded() &&
-                    getRTLTextPluginStatus() === 'deferred'
-                ) {
-                    downloadRTLTextPlugin();
-                }
-            }
 
             cacheEntryPossiblyAdded(this.dispatcher);