Add missing null check to getFullChunkIfLoaded

fixes #10915

patches/server/Chunk-System-Starlight-from-Moonrise.patch

@@ -25128,7 +25128,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    @Override
 +    public final LevelChunk moonrise$getFullChunkIfLoaded(final int chunkX, final int chunkZ) {
 +        final ca.spottedleaf.moonrise.patches.chunk_system.scheduling.NewChunkHolder newChunkHolder = this.moonrise$getChunkTaskScheduler().chunkHolderManager.getChunkHolder(ca.spottedleaf.moonrise.common.util.CoordinateUtils.getChunkKey(chunkX, chunkZ));
-+        if (!newChunkHolder.isFullChunkReady()) {
++        if (newChunkHolder == null || !newChunkHolder.isFullChunkReady()) {
 +            return null;
 +        }
 +