routers/repo: allow shorter SHA to download archive (#3834)

SHA length from 7-40 is now supported.

routers/repo/repo.go

@@ -311,14 +311,14 @@ func Download(ctx *context.Context) {
 			ctx.Handle(500, "GetTagCommit", err)
 			return
 		}
-	} else if len(refName) == 40 {
+	} else if len(refName) >= 7 && len(refName) <= 40 {
 		commit, err = gitRepo.GetCommit(refName)
 		if err != nil {
-			ctx.Handle(404, "GetCommit", nil)
+			ctx.NotFound()
 			return
 		}
 	} else {
-		ctx.Handle(404, "Download", nil)
+		ctx.NotFound()
 		return
 	}