Don't convert diff if in correct format

source/platforms/gitlab/GitLabGit.ts

@@ -27,14 +27,19 @@ export const gitlabChangesToDiff = (changes: GitLabMRChange[]): string => {
   // Gitlab doesn't return full raw git diff, relevant issue: https://gitlab.com/gitlab-org/gitlab/issues/24913
   return changes
     .map(change => {
+      const { diff } = change
+      if (diff.startsWith("diff --git a/") || diff.startsWith("--- a/") || diff.startsWith("--- /dev/null")) {
+        return diff
+      }
+
       return `\
 diff --git a/${change.old_path} b/${change.new_path}
 ${change.new_file ? `new file mode ${change.b_mode}` : ""}\
 ${change.deleted_file ? `deleted file mode ${change.a_mode}` : ""}\
 ${change.renamed_file ? `rename from ${change.old_path}\nrename to ${change.new_path}` : ""}
 --- ${change.new_file ? "/dev/null" : "a/" + change.old_path}
 +++ ${change.deleted_file ? "/dev/null" : "b/" + change.new_path}
-${change.diff}`
+${diff}`
     })
     .join("\n")
 }