Fix golangci-lint warnings (#17598 et al) (#17668)

Backport #17598 
Backport #17606 
Backport #17608 
Backport #17609

- Since https://gitea.com/gitea/test-env/pulls/10 the golangci-lint has been upgraded and is erroring about new warnings in the code, this PR fixes those warnings.

cmd/docs.go

@@ -43,7 +43,11 @@ func runDocs(ctx *cli.Context) error {
 		// Clean up markdown. The following bug was fixed in v2, but is present in v1.
 		// It affects markdown output (even though the issue is referring to man pages)
 		// https://github.com/urfave/cli/issues/1040
-		docs = docs[strings.Index(docs, "#"):]
+		firstHashtagIndex := strings.Index(docs, "#")
+
+		if firstHashtagIndex > 0 {
+			docs = docs[firstHashtagIndex:]
+		}
 	}
 
 	out := os.Stdout