op-batcher: Fix channelBuilder.OutputFrames to check for full channel

It only checked whether the input target was reached. But it should
also close the underlying channel out if it is full for any other
reason.

op-batcher/batcher/channel_builder.go

@@ -173,7 +173,7 @@ func (c *channelBuilder) setFullErr(err error) {
 // If the target has been reached, the channel is closed and all remaining
 // frames will be created, possibly with a small leftover frame.
 func (c *channelBuilder) OutputFrames() error {
-	if c.InputTargetReached() {
+	if c.IsFull() {
 		return c.closeAndOutputAllFrames()
 	}
 	return c.outputReadyFrames()