[Bitbucket DC]: Some PRs diff doesn't display original file

**Describe the bug**
Assumption that the main repository is named `zzz`, and the contributor's fork is named `zzz_fork`. Our main branch is called `xx-dev`.
If the source branch of a Pull Request is also named xx-dev (i.e., `zzz_fork/xx-dev` → `zzz/xx-dev`), the diff correctly shows the modified content. Otherwise (i.e., `zzz_fork/xx-compile` → `zzz/xx-dev`),, the diff only displays the entire modified file instead of the specific changes.

**To Reproduce**
1. Open a PR where the source branch name in the fork repository does not match the target branch name in the forked repository.

**Expected behavior**
The diff should clearly show the original version of the file along with the modified sections.

**Screenshots**
- PR that diff doesn't work in plugin
- The same PR in web browser
- Error in git output

- PR that diff works in plugin

**Environment and Version (please complete the following information):**
- Atlassian Plugin Version (3.6.0/3.4.17/3.4.20)
- Visual Studio Code Version (1.98.0)
Commit: 6609ac3d66f4eade5cf376d1cb76f13985724bcb
Date: 2025-03-04T21:06:18.612Z
Electron: 34.2.0
ElectronBuildId: 11044223
Chromium: 132.0.6834.196
Node.js: 20.18.2
V8: 13.2.152.36-electron.0
OS: Windows_NT x64 10.0.22621
- Is this a local or cloud environment? (Local)
- OS (linux)

**Additional context**
I have tried the plugin in version 3.6.0/3.4.17/3.4.20 but their behavior was consistent.

Reproduce the pull request diff with matching and non-matching source and target branch names, then inspect the reported Git output and error. Trace the TypeScript pull request diff flow from that failure; done means the original file and only its changed sections are displayed for forked branches with different names.

Written by the indexing model from the issue text.