Add missing parenthesis to max item size macro.

Oversight in commit 92f37505, per buildfarm.

src/backend/access/nbtree/nbtdedup.c

@@ -566,6 +566,8 @@ _bt_dedup_finish_pending(Page newpage, BTDedupState state)
 	{
 		/* Use original, unchanged base tuple */
 		tuplesz = IndexTupleSize(state->base);
+		Assert(tuplesz == MAXALIGN(IndexTupleSize(state->base)));
+		Assert(tuplesz <= BTMaxItemSize(newpage));
 		if (PageAddItem(newpage, (Item) state->base, tuplesz, tupoff,
 						false, false) == InvalidOffsetNumber)
 			elog(ERROR, "deduplication failed to add tuple to page");
@@ -585,6 +587,7 @@ _bt_dedup_finish_pending(Page newpage, BTDedupState state)
 		state->intervals[state->nintervals].nitems = state->nitems;
 
 		Assert(tuplesz == MAXALIGN(IndexTupleSize(final)));
+		Assert(tuplesz <= BTMaxItemSize(newpage));
 		if (PageAddItem(newpage, (Item) final, tuplesz, tupoff, false,
 						false) == InvalidOffsetNumber)
 			elog(ERROR, "deduplication failed to add tuple to page");

src/include/access/nbtree.h

@@ -162,10 +162,10 @@ typedef struct BTMetaPageData
  * attribute, which we account for here.
  */
 #define BTMaxItemSize(page) \
-	MAXALIGN_DOWN((PageGetPageSize(page) - \
-				   MAXALIGN(SizeOfPageHeaderData + 3*sizeof(ItemIdData)) - \
-				   MAXALIGN(sizeof(BTPageOpaqueData))) / 3) - \
-				   MAXALIGN(sizeof(ItemPointerData))
+	(MAXALIGN_DOWN((PageGetPageSize(page) - \
+					MAXALIGN(SizeOfPageHeaderData + 3*sizeof(ItemIdData)) - \
+					MAXALIGN(sizeof(BTPageOpaqueData))) / 3) - \
+					MAXALIGN(sizeof(ItemPointerData)))
 #define BTMaxItemSizeNoHeapTid(page) \
 	MAXALIGN_DOWN((PageGetPageSize(page) - \
 				   MAXALIGN(SizeOfPageHeaderData + 3*sizeof(ItemIdData)) - \