GetFeeds must always discard actions with dangling repo_id (#19598) (#19629)

Co-authored-by: Loïc Dachary <loic@dachary.org>
(cherry picked from commit b536b65189)

Conflicts:
        models/action_test.go
	  The GetFeeds function does not have a Context argument in 1.16.
	models/action.go
	  The SQL statement is essentially the same in 1.16 but
	  structured differently. The Join() was copied and the
   	  created_unix field prefixed with `action`.
	models/action_list.go
	  in 1.16 the loadRepoOwner method did not exist and
	  it was done in the RetrieveFeeds method of web/feed/profile.go.
          The safeguard to skip when act.Repo == nil was moved there.

models/action_test.go

@@ -129,3 +129,20 @@ func TestNotifyWatchers(t *testing.T) {
 		OpType:    action.OpType,
 	})
 }
+
+func TestGetFeedsCorrupted(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1}).(*user_model.User)
+	unittest.AssertExistsAndLoadBean(t, &Action{
+		ID:     8,
+		RepoID: 1700,
+	})
+
+	actions, err := GetFeeds(GetFeedsOptions{
+		RequestedUser:  user,
+		Actor:          user,
+		IncludePrivate: true,
+	})
+	assert.NoError(t, err)
+	assert.Len(t, actions, 0)
+}