Re: brininsert optimization opportunity

It seems that we have an oversight in this commit.  If there is no tuple
that has been inserted, we wouldn't have an available insert state in
the clean up phase.  So the Assert in brininsertcleanup() is not always
right.  For example:

regression=# update brin_summarize set value = brin_summarize.value;
server closed the connection unexpectedly

So I wonder if we should check 'bistate' and do the clean up only if
there is an available one, something like below.

--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -359,7 +359,9 @@ brininsertcleanup(IndexInfo *indexInfo)
 {
    BrinInsertState *bistate = (BrinInsertState *) indexInfo->ii_AmCache;

-   Assert(bistate);
+   /* We don't have an available insert state, nothing to do */
+   if (!bistate)
+       return;

Thanks
Richard