testing fix for channel data going black

Author: chrisj

src/chunk_manager/frontend.ts

@@ -326,6 +326,9 @@ function updateChunk(rpc: RPC, x: any) {
         `${source.rpcId} ${x.id} ${x.state} with chunkDataSize ${x.chunkDataSize}`,
     );
   }
+  if (!source) {
+    return; // DEBUGGING
+  }
   const queueManager = source.chunkManager.chunkQueueManager;
   if (source.immediateChunkUpdates) {
     if (queueManager.applyChunkUpdate(x)) {