Update iterateAllChunks docs to mention duplicates

Author: macneale4

go/store/nbs/table.go

@@ -265,11 +265,13 @@ type chunkSource interface {
 	// currentSize returns the current total physical size of the chunkSource.
 	currentSize() uint64
 
-	// scanAllChunks will call the provided function for each chunk in the chunkSource. This is currently used
+	// iterateAllChunks will call the provided function for each chunk in the chunkSource. This is currently used
 	// to perform integrity checks, and the chunk passed in will have the address from the index, and the content
-	// loaded. This iterator doesn't have a way to stop the iteration other than the context being canceled.
+	// loaded. Note that there may be duplicate chunks in the chunkSource, so the callback may be called multiple times
+	// with the same chunk id and content.
 	//
-	// If there is a failure reading the chunk, the error will be returned - note that this can happen in the middle of
+	// This iterator doesn't have a way to stop the iteration other than the context being canceled. If there is a failure
+	// reading the chunk, the error will be returned - note that this can happen in the middle of
 	// the scan, and will likely mean that the scan didn't complete. Note that errors returned by this method are not
 	// related to the callback - if the callback discovers an error, it must manage that out of band.
 	iterateAllChunks(context.Context, func(chunk chunks.Chunk), *Stats) error