Use correct ChunkHolder map for off-thread access

Not sure why updating was used. Looks like a bad change
resulting from the Mojang mappings changes.

Fixes PaperMC#102

src/main/java/ca/spottedleaf/starlight/mixin/common/world/ServerWorldMixin.java

@@ -37,7 +37,7 @@ protected ServerWorldMixin(final WritableLevelData writableLevelData, final Reso
     @Override
     public final LevelChunk getChunkAtImmediately(final int chunkX, final int chunkZ) {
         final ChunkMap storage = this.chunkSource.chunkMap;
-        final ChunkHolder holder = storage.getUpdatingChunkIfPresent(CoordinateUtils.getChunkKey(chunkX, chunkZ));
+        final ChunkHolder holder = storage.getVisibleChunkIfPresent(CoordinateUtils.getChunkKey(chunkX, chunkZ));
 
         if (holder == null) {
             return null;
@@ -51,7 +51,7 @@ public final LevelChunk getChunkAtImmediately(final int chunkX, final int chunkZ
     @Override
     public final ChunkAccess getAnyChunkImmediately(final int chunkX, final int chunkZ) {
         final ChunkMap storage = this.chunkSource.chunkMap;
-        final ChunkHolder holder = storage.getUpdatingChunkIfPresent(CoordinateUtils.getChunkKey(chunkX, chunkZ));
+        final ChunkHolder holder = storage.getVisibleChunkIfPresent(CoordinateUtils.getChunkKey(chunkX, chunkZ));
 
         return holder == null ? null : holder.getLastAvailable();
     }