Fix bug in lossy-page handling in GIN

When returning rows from a bitmap, as done with partial match queries, we
would get stuck in an infinite loop if the bitmap contained a lossy page
reference.

This bug is new in master, it was introduced by the patch to allow skipping
items refuted by other entries in GIN scans.

Report and fix by Alexander Korotkov

src/backend/access/gin/ginget.c

@@ -741,7 +741,9 @@ entryGetItem(GinState *ginstate, GinScanEntry entry,
 			while (entry->matchResult == NULL ||
 				   (entry->matchResult->ntuples >= 0 &&
 					entry->offset >= entry->matchResult->ntuples) ||
-				   entry->matchResult->blockno < advancePastBlk)
+				   entry->matchResult->blockno < advancePastBlk ||
+				   (ItemPointerIsLossyPage(&advancePast) &&
+					entry->matchResult->blockno == advancePastBlk))
 			{
 				entry->matchResult = tbm_iterate(entry->matchIterator);