Gogs: DoS in rendering issue index pattern

Gogs is an open source self-hosted Git service. Prior to 0.14.3, specially crafted issue index pattern can cause a panic when rendering, resulting in denial of service. In internal/markup/markup.go, RenderIssueIndexPattern renders the issue index pattern to a link using com.Expand, which is not safe: when the configured pattern contains an opening brace { but no closing brace }, strings.Index(template, "}") returns -1 and the subsequent slice template[:-1] triggers a panic. Once such a pattern is set, any page in the affected repository that contains an issue index reference such as #1 becomes unavailable. This vulnerability is fixed in 0.14.3.