Improve error handling and fix test realism

- Use IsErrPullRequestNotExist for proper error handling
- Remove redundant nil check (guaranteed after successful load)
- Fix test to use different commit SHAs (realistic Git scenario)
- All tests still passing

Co-authored-by: silverwind <115237+silverwind@users.noreply.github.com>

Author: Copilot

services/issue/commit.go

@@ -161,8 +161,10 @@ func UpdateIssuesCommit(ctx context.Context, doer *user_model.User, repo *repo_m
 			// Skip self-references: if this commit is the merge commit of the PR it references
 			if refIssue.IsPull {
 				if err := refIssue.LoadPullRequest(ctx); err != nil {
-					log.Error("LoadPullRequest: %v", err)
-				} else if refIssue.PullRequest != nil && refIssue.PullRequest.MergedCommitID == c.Sha1 {
+					if !issues_model.IsErrPullRequestNotExist(err) {
+						log.Error("LoadPullRequest: %v", err)
+					}
+				} else if refIssue.PullRequest.MergedCommitID == c.Sha1 {
 					// This is a self-reference (PR merge commit referencing its own PR), skip it
 					continue
 				}

services/issue/commit_test.go

@@ -332,22 +332,23 @@ func TestUpdateIssuesCommit_SelfReference(t *testing.T) {
 	unittest.AssertNotExistsBean(t, selfRefCommentBean)
 	unittest.CheckConsistencyFor(t, &activities_model.Action{})
 
-	// Test that the same merge commit can still create references to other issues
+	// Test that normal (non-self-referencing) commit comments are still created
+	// Use a different commit that is NOT a merge commit for any PR
 	pushCommits2 := []*repository.PushCommit{
 		{
-			Sha1:           "1a8823cd1a9549fde083f992f6b9b87a7ab74fb3",
+			Sha1:           "abcdef9876543210", // Different commit, not a merge commit
 			CommitterEmail: "user2@example.com",
 			CommitterName:  "User Two",
 			AuthorEmail:    "user2@example.com",
 			AuthorName:     "User Two",
-			Message:        "Merge pull request (#2) - also fixes #1", // References a different issue
+			Message:        "Fix bug, refs #1", // References issue #1
 		},
 	}
 
-	// This comment SHOULD be created (reference to a different issue)
+	// This comment SHOULD be created (reference to a different issue from a non-merge commit)
 	otherRefCommentBean := &issues_model.Comment{
 		Type:      issues_model.CommentTypeCommitRef,
-		CommitSHA: "1a8823cd1a9549fde083f992f6b9b87a7ab74fb3",
+		CommitSHA: "abcdef9876543210",
 		PosterID:  user.ID,
 		IssueID:   1, // References issue #1
 	}