[GITEA] Check for Commit in opengraph

- Backport of #2094
- It's possible that `PageIsDiff` is set but not `Commit` resulting in a
NPE in the template. This can happen when the requested commit doesn't exist.
- Regression of c802c46a9b &
5743d7cb5b
- Added 'hacky' integration test.

(cherry picked from commit 8db2d5e4a7)

templates/base/head_opengraph.tmpl

@@ -17,7 +17,7 @@
 	{{else if or .PageIsDiff .IsViewFile}}
 		<meta property="og:title" content="{{.Title}}">
 		<meta property="og:url" content="{{AppUrl}}{{.Link}}">
-		{{if .PageIsDiff}}
+		{{if and .PageIsDiff .Commit}}
 			{{- $commitMessageParts := StringUtils.Cut .Commit.Message "\n" -}}
 			{{- $commitMessageBody := index $commitMessageParts 1 -}}
 			{{- if $commitMessageBody -}}

tests/integration/repo_test.go

@@ -729,3 +729,20 @@ func TestArchiveRequest(t *testing.T) {
 	req := NewRequest(t, "GET", "/user2/repo1/archive/a480fe666d6f550787b6cc85047b966d1f8d6bbf.zip")
 	session.MakeRequest(t, req, http.StatusNotFound)
 }
+
+func TestCommitView(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	t.Run("Non-existent commit", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		req := NewRequest(t, "GET", "/user2/repo1/commit/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+		MakeRequest(t, req, http.StatusNotFound)
+		req.Header.Add("Accept", "text/html")
+		resp := MakeRequest(t, req, http.StatusNotFound)
+
+		// Really ensure that 404 is being sent back.
+		doc := NewHTMLParser(t, resp.Body)
+		doc.AssertElement(t, `[aria-label="Page Not Found"]`, true)
+	})
+}