[GITEA] Fix NPE in UsernameSubRoute

- When the user is not found in `reloadparam`, early return when the
user is not found to avoid calling `IsUserVisibleToViewer` which in turn
avoids causing a NPE.
- This fixes the case that a 500 error and 404 error is shown on the
same page.
- Add integration test for non-existant user RSS.
- Regression by c6366089df

(cherry picked from commit f0e0696278)
(cherry picked from commit 75d8066908)
(cherry picked from commit 4d0a1e0637)
(cherry picked from commit 5f40a485da)
(cherry picked from commit c4cb7812e3)
(cherry picked from commit d31ce2f03d)
(cherry picked from commit cfebef4f82)

routers/web/user/home.go

@@ -715,12 +715,15 @@ func UsernameSubRoute(ctx *context.Context) {
 	reloadParam := func(suffix string) (success bool) {
 		ctx.SetParams("username", strings.TrimSuffix(username, suffix))
 		context_service.UserAssignmentWeb()(ctx)
+		if ctx.Written() {
+			return false
+		}
 		// check view permissions
 		if !user_model.IsUserVisibleToViewer(ctx, ctx.ContextUser, ctx.Doer) {
 			ctx.NotFound("user", fmt.Errorf(ctx.ContextUser.Name))
 			return false
 		}
-		return !ctx.Written()
+		return true
 	}
 	switch {
 	case strings.HasSuffix(username, ".png"):

tests/integration/user_test.go

@@ -243,6 +243,9 @@ func testExportUserGPGKeys(t *testing.T, user, expected string) {
 }
 
 func TestGetUserRss(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	t.Run("Normal", func(t *testing.T) {
 		user34 := "the_34-user.with.all.allowedChars"
 		req := NewRequestf(t, "GET", "/%s.rss", user34)
 		resp := MakeRequest(t, req, http.StatusOK)
@@ -253,6 +256,12 @@ func TestGetUserRss(t *testing.T) {
 			description, _ := rssDoc.ChildrenFiltered("description").Html()
 			assert.EqualValues(t, "<p dir="auto">some <a href="https://commonmark.org/" rel="nofollow">commonmark</a>!</p>\n", description)
 		}
+	})
+	t.Run("Non-existent user", func(t *testing.T) {
+		session := loginUser(t, "user2")
+		req := NewRequestf(t, "GET", "/non-existent-user.rss")
+		session.MakeRequest(t, req, http.StatusNotFound)
+	})
 }
 
 func TestListStopWatches(t *testing.T) {