Validate Issue Index before querying DB (#16406)

models/issue.go

@@ -1018,6 +1018,9 @@ func NewIssue(repo *Repository, issue *Issue, labelIDs []int64, uuids []string)
 
 // GetIssueByIndex returns raw issue without loading attributes by index in a repository.
 func GetIssueByIndex(repoID, index int64) (*Issue, error) {
+	if index < 1 {
+		return nil, ErrIssueNotExist{}
+	}
 	issue := &Issue{
 		RepoID: repoID,
 		Index:  index,