client: fix Paginate's arguments validation (#6205)

Check both page and defLimit against negative values.

Follow up of #6205

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

client/utils.go

@@ -2,15 +2,22 @@ package client
 
 // Paginate returns the correct starting and ending index for a paginated query,
 // given that client provides a desired page and limit of objects and the handler
-// provides the total number of objects. If the start page is invalid, non-positive
-// values are returned signaling the request is invalid.
-//
-// NOTE: The start page is assumed to be 1-indexed.
+// provides the total number of objects. The start page is assumed to be 1-indexed.
+// If the start page is invalid, non-positive values are returned signaling the
+// request is invalid; it returns non-positive values if limit is non-positive and
+// defLimit is negative.
 func Paginate(numObjs, page, limit, defLimit int) (start, end int) {
-	if page == 0 {
+	if page <= 0 {
 		// invalid start page
 		return -1, -1
-	} else if limit == 0 {
+	}
+
+	// fallback to default limit if supplied limit is invalid
+	if limit <= 0 {
+		if defLimit < 0 {
+			// invalid default limit
+			return -1, -1
+		}
 		limit = defLimit
 	}