lab: Use HeadSHA value when CommitID is not specified

In some cases note.CommitID is not set.  In these cases AFAICT the
note.Position.HeadSHA value does correctly point to the commented on
commit and the rest of the data is correct.

Use the HeadSHA value when the CommitID is not specified.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>

cmd/show_common.go

@@ -173,24 +173,31 @@ func displayCommitDiscussion(project string, idNum int, note *gitlab.Note) {
 	//
 	// I am leaving this comment here in case it ever changes again.
 
+	// In some cases the CommitID field is still not populated correctly.
+	// In those cases use the HeadSHA value instead of the CommitID.
+	commitID := note.CommitID
+	if commitID == "" {
+		commitID = note.Position.HeadSHA
+	}
+
 	// Get a unified diff for the entire file
-	ds, err := lab.GetCommitDiff(project, note.CommitID)
+	ds, err := lab.GetCommitDiff(project, commitID)
 	if err != nil {
-		fmt.Printf("    Could not get diff for commit %s.\n", note.CommitID)
+		fmt.Printf("    Could not get diff for commit %s.\n", commitID)
 		return
 	}
 
 	if len(ds) == 0 {
-		log.Fatal("    No diff found for %s.", note.CommitID)
+		log.Fatal("    No diff found for %s.", commitID)
 	}
 
 	// In general, only have to display the NewPath, however there
 	// are some unusual cases where the OldPath may be displayed
 	if note.Position.NewPath == note.Position.OldPath {
-		fmt.Println("commit:" + note.CommitID)
+		fmt.Println("commit:" + commitID)
 		fmt.Println("File:" + note.Position.NewPath)
 	} else {
-		fmt.Println("commit:" + note.CommitID)
+		fmt.Println("commit:" + commitID)
 		fmt.Println("Files[old:" + note.Position.OldPath + " new:" + note.Position.NewPath + "]")
 	}