fix(xrefs_filter): properly merge page lists that represent allPages (#…

…5624)

Previously, uint32max, which represents the set of all pages, was being merged into the list of page indices and later used as an array index, which was out of bounds.

kythe/go/serving/xrefs/xrefs_filter.go

@@ -261,6 +261,9 @@ func postingAnd(idx postings, list []uint32, trigram uint32) []uint32 {
 }
 
 func mergeOr(l1, l2 []uint32) []uint32 {
+	if isAllPages(l1) || isAllPages(l2) {
+		return allPages
+	}
 	var l []uint32
 	var i, j int
 	for i < len(l1) || j < len(l2) {